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 $207.86   9.484%   $227.5734   $227.57   $227.55   $227.60  
  Purchase #2 $51.62   13.410%   $58.5422   $58.54   $58.55   $58.50  
  Purchase #3 $201.74   12.727%   $227.4154   $227.42   $227.40   $227.40  
  Purchase #4 $41.31   13.587%   $46.9228   $46.92   $46.90   $46.90  
  Purchase #5 $232.46   9.668%   $254.9342   $254.93   $254.95   $254.90  
  Purchase #6 $205.97   4.507%   $215.2531   $215.25   $215.25   $215.30  
  Purchase #7 $7.71   9.647%   $8.4538   $8.45   $8.45   $8.50  
  7 purchase totals = $948.67       $1,039.0949   $1,039.08   $1,039.05   $1,039.10