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 $62.67   9.208%   $68.4407   $68.44   $68.45   $68.40  
  Purchase #2 $210.61   8.592%   $228.7056   $228.71   $228.70   $228.70  
  Purchase #3 $23.35   5.350%   $24.5992   $24.60   $24.60   $24.60  
  Purchase #4 $112.96   6.765%   $120.6017   $120.60   $120.60   $120.60  
  Purchase #5 $144.69   9.785%   $158.8479   $158.85   $158.85   $158.80  
  Purchase #6 $223.51   3.600%   $231.5564   $231.56   $231.55   $231.60  
  Purchase #7 $173.39   5.481%   $182.8935   $182.89   $182.90   $182.90  
  7 purchase totals = $951.18       $1,015.6450   $1,015.65   $1,015.65   $1,015.60