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 $150.90   12.427%   $169.6523   $169.65   $169.65   $169.70  
  Purchase #2 $133.51   9.376%   $146.0279   $146.03   $146.05   $146.00  
  Purchase #3 $165.48   6.353%   $175.9929   $175.99   $176.00   $176.00  
  Purchase #4 $156.44   7.231%   $167.7522   $167.75   $167.75   $167.80  
  Purchase #5 $62.31   11.744%   $69.6277   $69.63   $69.65   $69.60  
  Purchase #6 $226.43   9.199%   $247.2593   $247.26   $247.25   $247.30  
  Purchase #7 $211.44   4.377%   $220.6947   $220.69   $220.70   $220.70  
  7 purchase totals = $1,106.51       $1,197.0070   $1,197.00   $1,197.05   $1,197.10