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 $234.42   4.791%   $245.6511   $245.65   $245.65   $245.70  
  Purchase #2 $53.45   9.203%   $58.369   $58.37   $58.35   $58.40  
  Purchase #3 $227.28   5.120%   $238.9167   $238.92   $238.90   $238.90  
  Purchase #4 $206.55   3.859%   $214.5208   $214.52   $214.50   $214.50  
  Purchase #5 $94.65   11.325%   $105.3691   $105.37   $105.35   $105.40  
  Purchase #6 $212.45   7.650%   $228.7024   $228.70   $228.70   $228.70  
  Purchase #7 $175.40   10.623%   $194.0327   $194.03   $194.05   $194.00  
  7 purchase totals = $1,204.20       $1,285.5618   $1,285.56   $1,285.50   $1,285.60