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 $94.52   10.378%   $104.3293   $104.33   $104.35   $104.30  
  Purchase #2 $78.93   9.272%   $86.2484   $86.25   $86.25   $86.20  
  Purchase #3 $224.51   9.336%   $245.4703   $245.47   $245.45   $245.50  
  Purchase #4 $10.79   8.688%   $11.7274   $11.73   $11.75   $11.70  
  Purchase #5 $111.49   12.601%   $125.5389   $125.54   $125.55   $125.50  
  Purchase #6 $162.57   8.255%   $175.9902   $175.99   $176.00   $176.00  
  Purchase #7 $47.61   7.726%   $51.2883   $51.29   $51.30   $51.30  
  7 purchase totals = $730.42       $800.5928   $800.60   $800.65   $800.50