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 $193.93   11.352%   $215.9449   $215.94   $215.95   $215.90  
  Purchase #2 $119.37   10.190%   $131.5338   $131.53   $131.55   $131.50  
  Purchase #3 $246.36   9.605%   $270.0229   $270.02   $270.00   $270.00  
  Purchase #4 $133.65   5.497%   $140.9967   $141.00   $141.00   $141.00  
  Purchase #5 $187.90   3.786%   $195.0139   $195.01   $195.00   $195.00  
  Purchase #6 $56.51   11.604%   $63.0674   $63.07   $63.05   $63.10  
  Purchase #7 $60.79   9.833%   $66.7675   $66.77   $66.75   $66.80  
  7 purchase totals = $998.51       $1,083.3471   $1,083.34   $1,083.30   $1,083.30