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 $217.45   8.151%   $235.1743   $235.17   $235.15   $235.20  
  Purchase #2 $69.50   9.177%   $75.878   $75.88   $75.90   $75.90  
  Purchase #3 $200.51   6.163%   $212.8674   $212.87   $212.85   $212.90  
  Purchase #4 $161.65   7.576%   $173.8966   $173.90   $173.90   $173.90  
  Purchase #5 $209.98   5.725%   $222.0014   $222.00   $222.00   $222.00  
  Purchase #6 $105.61   7.230%   $113.2456   $113.25   $113.25   $113.20  
  Purchase #7 $243.90   10.384%   $269.2266   $269.23   $269.25   $269.20  
  7 purchase totals = $1,208.60       $1,302.2899   $1,302.30   $1,302.30   $1,302.30