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 $61.51   3.796%   $63.8449   $63.84   $63.85   $63.80  
  Purchase #2 $90.32   8.360%   $97.8708   $97.87   $97.85   $97.90  
  Purchase #3 $133.90   11.119%   $148.7883   $148.79   $148.80   $148.80  
  Purchase #4 $236.26   8.275%   $255.8105   $255.81   $255.80   $255.80  
  Purchase #5 $132.60   10.175%   $146.0921   $146.09   $146.10   $146.10  
  Purchase #6 $234.49   12.829%   $264.5727   $264.57   $264.55   $264.60  
  Purchase #7 $43.25   6.705%   $46.1499   $46.15   $46.15   $46.10  
  7 purchase totals = $932.33       $1,023.1292   $1,023.12   $1,023.10   $1,023.10