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 $146.95   13.684%   $167.0586   $167.06   $167.05   $167.10  
  Purchase #2 $56.74   3.812%   $58.9029   $58.90   $58.90   $58.90  
  Purchase #3 $29.74   11.826%   $33.2571   $33.26   $33.25   $33.30  
  Purchase #4 $36.74   8.821%   $39.9808   $39.98   $40.00   $40.00  
  Purchase #5 $247.33   13.631%   $281.0436   $281.04   $281.05   $281.00  
  Purchase #6 $241.49   11.525%   $269.3217   $269.32   $269.30   $269.30  
  Purchase #7 $193.43   8.782%   $210.417   $210.42   $210.40   $210.40  
  7 purchase totals = $952.42       $1,059.9817   $1,059.98   $1,059.95   $1,060.00