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 $32.95   8.208%   $35.6545   $35.65   $35.65   $35.70  
  Purchase #2 $241.78   10.461%   $267.0726   $267.07   $267.05   $267.10  
  Purchase #3 $107.50   9.335%   $117.5351   $117.54   $117.55   $117.50  
  Purchase #4 $25.91   12.125%   $29.0516   $29.05   $29.05   $29.10  
  Purchase #5 $24.32   8.738%   $26.4451   $26.45   $26.45   $26.40  
  Purchase #6 $218.55   4.219%   $227.7706   $227.77   $227.75   $227.80  
  Purchase #7 $182.36   11.198%   $202.7807   $202.78   $202.80   $202.80  
  7 purchase totals = $833.37       $906.3102   $906.31   $906.30   $906.40