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 $61.54   12.471%   $69.2147   $69.21   $69.20   $69.20  
  Purchase #2 $115.97   8.586%   $125.9272   $125.93   $125.95   $125.90  
  Purchase #3 $229.33   5.786%   $242.599   $242.60   $242.60   $242.60  
  Purchase #4 $58.92   6.322%   $62.6449   $62.64   $62.65   $62.60  
  Purchase #5 $30.87   9.427%   $33.7801   $33.78   $33.80   $33.80  
  Purchase #6 $155.95   13.631%   $177.2075   $177.21   $177.20   $177.20  
  Purchase #7 $74.51   7.778%   $80.3054   $80.31   $80.30   $80.30  
  7 purchase totals = $727.09       $791.6788   $791.68   $791.70   $791.60