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 $33.53   5.241%   $35.2873   $35.29   $35.30   $35.30  
  Purchase #2 $145.31   4.392%   $151.692   $151.69   $151.70   $151.70  
  Purchase #3 $47.53   8.147%   $51.4023   $51.40   $51.40   $51.40  
  Purchase #4 $171.77   4.300%   $179.1561   $179.16   $179.15   $179.20  
  Purchase #5 $214.84   5.139%   $225.8806   $225.88   $225.90   $225.90  
  Purchase #6 $180.69   12.606%   $203.4678   $203.47   $203.45   $203.50  
  Purchase #7 $141.55   5.430%   $149.2362   $149.24   $149.25   $149.20  
  7 purchase totals = $935.22       $996.1223   $996.13   $996.15   $996.20