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 $163.54   12.241%   $183.5589   $183.56   $183.55   $183.60  
  Purchase #2 $218.38   4.547%   $228.3097   $228.31   $228.30   $228.30  
  Purchase #3 $119.47   3.807%   $124.0182   $124.02   $124.00   $124.00  
  Purchase #4 $229.41   11.499%   $255.7899   $255.79   $255.80   $255.80  
  Purchase #5 $62.66   9.223%   $68.4391   $68.44   $68.45   $68.40  
  Purchase #6 $67.81   9.392%   $74.1787   $74.18   $74.20   $74.20  
  Purchase #7 $16.27   11.301%   $18.1087   $18.11   $18.10   $18.10  
  7 purchase totals = $877.54       $952.4032   $952.41   $952.40   $952.40