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 $78.46   3.263%   $81.0201   $81.02   $81.00   $81.00  
  Purchase #2 $204.73   9.753%   $224.6973   $224.70   $224.70   $224.70  
  Purchase #3 $237.93   7.313%   $255.3298   $255.33   $255.35   $255.30  
  Purchase #4 $104.36   7.381%   $112.0628   $112.06   $112.05   $112.10  
  Purchase #5 $26.85   3.785%   $27.8663   $27.87   $27.85   $27.90  
  Purchase #6 $57.64   7.851%   $62.1653   $62.17   $62.15   $62.20  
  Purchase #7 $162.81   9.820%   $178.7979   $178.80   $178.80   $178.80  
  7 purchase totals = $872.78       $941.9395   $941.95   $941.90   $942.00