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 $225.76   4.646%   $236.2488   $236.25   $236.25   $236.20  
  Purchase #2 $131.52   3.169%   $135.6879   $135.69   $135.70   $135.70  
  Purchase #3 $57.55   9.846%   $63.2164   $63.22   $63.20   $63.20  
  Purchase #4 $60.56   5.112%   $63.6558   $63.66   $63.65   $63.70  
  Purchase #5 $199.98   7.765%   $215.5084   $215.51   $215.50   $215.50  
  Purchase #6 $126.95   5.638%   $134.1074   $134.11   $134.10   $134.10  
  Purchase #7 $215.64   5.596%   $227.7072   $227.71   $227.70   $227.70  
  7 purchase totals = $1,017.96       $1,076.1319   $1,076.15   $1,076.10   $1,076.10