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 $217.42   3.413%   $224.8405   $224.84   $224.85   $224.80  
  Purchase #2 $116.69   3.326%   $120.5711   $120.57   $120.55   $120.60  
  Purchase #3 $56.35   6.467%   $59.9942   $59.99   $60.00   $60.00  
  Purchase #4 $39.42   13.533%   $44.7547   $44.75   $44.75   $44.80  
  Purchase #5 $216.87   7.149%   $232.374   $232.37   $232.35   $232.40  
  Purchase #6 $51.67   7.304%   $55.444   $55.44   $55.45   $55.40  
  Purchase #7 $67.52   12.203%   $75.7595   $75.76   $75.75   $75.80  
  7 purchase totals = $765.94       $813.7380   $813.72   $813.70   $813.80