Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $162.29   10.731%   $179.7053   $179.71   $179.70   $179.70  
  Purchase #2 $156.99   7.644%   $168.9903   $168.99   $169.00   $169.00  
  Purchase #3 $115.34   8.607%   $125.2673   $125.27   $125.25   $125.30  
  Purchase #4 $144.69   11.149%   $160.8215   $160.82   $160.80   $160.80  
  Purchase #5 $146.79   12.801%   $165.5806   $165.58   $165.60   $165.60  
  Purchase #6 $241.68   9.391%   $264.3762   $264.38   $264.40   $264.40  
  Purchase #7 $203.31   13.594%   $230.948   $230.95   $230.95   $230.90  
  7 purchase totals = $1,171.09       $1,295.6892   $1,295.70   $1,295.70   $1,295.70