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 $143.98   13.166%   $162.9364   $162.94   $162.95   $162.90  
  Purchase #2 $129.87   4.155%   $135.2661   $135.27   $135.25   $135.30  
  Purchase #3 $70.90   6.162%   $75.2689   $75.27   $75.25   $75.30  
  Purchase #4 $22.49   8.129%   $24.3182   $24.32   $24.30   $24.30  
  Purchase #5 $186.63   10.709%   $206.6162   $206.62   $206.60   $206.60  
  Purchase #6 $160.46   6.432%   $170.7808   $170.78   $170.80   $170.80  
  Purchase #7 $167.67   4.814%   $175.7416   $175.74   $175.75   $175.70  
  7 purchase totals = $882.00       $950.9282   $950.94   $950.90   $950.90