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 $236.27   6.827%   $252.4002   $252.40   $252.40   $252.40  
  Purchase #2 $216.42   5.794%   $228.9594   $228.96   $228.95   $229.00  
  Purchase #3 $68.91   11.549%   $76.8684   $76.87   $76.85   $76.90  
  Purchase #4 $86.96   8.472%   $94.3273   $94.33   $94.35   $94.30  
  Purchase #5 $168.27   12.669%   $189.5881   $189.59   $189.60   $189.60  
  Purchase #6 $183.36   7.651%   $197.3889   $197.39   $197.40   $197.40  
  Purchase #7 $50.95   6.374%   $54.1976   $54.20   $54.20   $54.20  
  7 purchase totals = $1,011.14       $1,093.7299   $1,093.74   $1,093.75   $1,093.80