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 $86.28   12.105%   $96.7242   $96.72   $96.70   $96.70  
  Purchase #2 $176.93   11.200%   $196.7462   $196.75   $196.75   $196.70  
  Purchase #3 $104.93   5.448%   $110.6466   $110.65   $110.65   $110.60  
  Purchase #4 $166.41   6.656%   $177.4862   $177.49   $177.50   $177.50  
  Purchase #5 $62.42   3.488%   $64.5972   $64.60   $64.60   $64.60  
  Purchase #6 $234.29   4.229%   $244.1981   $244.20   $244.20   $244.20  
  Purchase #7 $86.71   7.341%   $93.0754   $93.08   $93.10   $93.10  
  7 purchase totals = $917.97       $983.4739   $983.49   $983.50   $983.40