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 $246.98   10.253%   $272.3029   $272.30   $272.30   $272.30  
  Purchase #2 $97.28   6.829%   $103.9233   $103.92   $103.90   $103.90  
  Purchase #3 $143.45   11.296%   $159.6541   $159.65   $159.65   $159.70  
  Purchase #4 $118.46   12.210%   $132.924   $132.92   $132.90   $132.90  
  Purchase #5 $62.99   6.731%   $67.2299   $67.23   $67.25   $67.20  
  Purchase #6 $154.98   7.282%   $166.2656   $166.27   $166.25   $166.30  
  Purchase #7 $22.59   9.444%   $24.7234   $24.72   $24.70   $24.70  
  7 purchase totals = $846.73       $927.0232   $927.01   $926.95   $927.00