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 $73.49   5.217%   $77.324   $77.32   $77.30   $77.30  
  Purchase #2 $51.69   6.717%   $55.162   $55.16   $55.15   $55.20  
  Purchase #3 $129.83   7.498%   $139.5647   $139.56   $139.55   $139.60  
  Purchase #4 $71.48   5.816%   $75.6373   $75.64   $75.65   $75.60  
  Purchase #5 $71.33   12.628%   $80.3376   $80.34   $80.35   $80.30  
  Purchase #6 $10.85   8.402%   $11.7616   $11.76   $11.75   $11.80  
  Purchase #7 $245.37   6.544%   $261.427   $261.43   $261.45   $261.40  
  7 purchase totals = $654.04       $701.2142   $701.21   $701.20   $701.20