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 $206.99   9.809%   $227.2936   $227.29   $227.30   $227.30  
  Purchase #2 $47.59   13.533%   $54.0304   $54.03   $54.05   $54.00  
  Purchase #3 $46.80   10.669%   $51.7931   $51.79   $51.80   $51.80  
  Purchase #4 $86.44   8.199%   $93.5272   $93.53   $93.55   $93.50  
  Purchase #5 $110.69   9.406%   $121.1015   $121.10   $121.10   $121.10  
  Purchase #6 $186.35   10.544%   $205.9987   $206.00   $206.00   $206.00  
  Purchase #7 $62.85   10.698%   $69.5737   $69.57   $69.55   $69.60  
  7 purchase totals = $747.71       $823.3182   $823.31   $823.35   $823.30