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 $131.89   10.366%   $145.5617   $145.56   $145.55   $145.60  
  Purchase #2 $101.32   12.156%   $113.6365   $113.64   $113.65   $113.60  
  Purchase #3 $121.59   3.299%   $125.6013   $125.60   $125.60   $125.60  
  Purchase #4 $210.27   10.395%   $232.1276   $232.13   $232.15   $232.10  
  Purchase #5 $191.50   12.767%   $215.9488   $215.95   $215.95   $215.90  
  Purchase #6 $46.45   11.232%   $51.6673   $51.67   $51.65   $51.70  
  Purchase #7 $126.79   10.505%   $140.1093   $140.11   $140.10   $140.10  
  7 purchase totals = $929.81       $1,024.6525   $1,024.66   $1,024.65   $1,024.60