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 $174.84   11.655%   $195.2176   $195.22   $195.20   $195.20  
  Purchase #2 $61.40   10.132%   $67.621   $67.62   $67.60   $67.60  
  Purchase #3 $185.29   8.467%   $200.9785   $200.98   $201.00   $201.00  
  Purchase #4 $97.83   4.854%   $102.5787   $102.58   $102.60   $102.60  
  Purchase #5 $143.67   9.759%   $157.6908   $157.69   $157.70   $157.70  
  Purchase #6 $28.82   11.474%   $32.1268   $32.13   $32.15   $32.10  
  Purchase #7 $100.60   3.434%   $104.0546   $104.05   $104.05   $104.10  
  7 purchase totals = $792.45       $860.2680   $860.27   $860.30   $860.30