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 $125.96   12.607%   $141.8398   $141.84   $141.85   $141.80  
  Purchase #2 $184.78   9.227%   $201.8297   $201.83   $201.85   $201.80  
  Purchase #3 $49.49   13.428%   $56.1355   $56.14   $56.15   $56.10  
  Purchase #4 $158.57   4.582%   $165.8357   $165.84   $165.85   $165.80  
  Purchase #5 $189.28   11.620%   $211.2743   $211.27   $211.25   $211.30  
  Purchase #6 $12.42   10.206%   $13.6876   $13.69   $13.70   $13.70  
  Purchase #7 $164.57   3.769%   $170.7726   $170.77   $170.75   $170.80  
  7 purchase totals = $885.07       $961.3752   $961.38   $961.40   $961.30