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 $209.28   6.673%   $223.2453   $223.25   $223.25   $223.20  
  Purchase #2 $170.29   10.533%   $188.2266   $188.23   $188.25   $188.20  
  Purchase #3 $122.37   9.770%   $134.3255   $134.33   $134.35   $134.30  
  Purchase #4 $67.73   11.850%   $75.756   $75.76   $75.75   $75.80  
  Purchase #5 $72.98   11.267%   $81.2027   $81.20   $81.20   $81.20  
  Purchase #6 $187.80   6.307%   $199.6445   $199.64   $199.65   $199.60  
  Purchase #7 $119.64   12.253%   $134.2995   $134.30   $134.30   $134.30  
  7 purchase totals = $950.09       $1,036.7001   $1,036.71   $1,036.75   $1,036.60