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 $216.75   10.187%   $238.8303   $238.83   $238.85   $238.80  
  Purchase #2 $197.87   12.481%   $222.5662   $222.57   $222.55   $222.60  
  Purchase #3 $229.39   12.162%   $257.2884   $257.29   $257.30   $257.30  
  Purchase #4 $51.53   6.226%   $54.7383   $54.74   $54.75   $54.70  
  Purchase #5 $17.35   12.128%   $19.4542   $19.45   $19.45   $19.50  
  Purchase #6 $85.39   10.139%   $94.0477   $94.05   $94.05   $94.00  
  Purchase #7 $187.66   11.204%   $208.6854   $208.69   $208.70   $208.70  
  7 purchase totals = $985.94       $1,095.6105   $1,095.62   $1,095.65   $1,095.60