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 $56.73   9.310%   $62.0116   $62.01   $62.00   $62.00  
  Purchase #2 $202.50   13.402%   $229.6391   $229.64   $229.65   $229.60  
  Purchase #3 $84.73   6.153%   $89.9434   $89.94   $89.95   $89.90  
  Purchase #4 $185.64   12.788%   $209.3796   $209.38   $209.40   $209.40  
  Purchase #5 $184.75   11.277%   $205.5843   $205.58   $205.60   $205.60  
  Purchase #6 $27.80   8.388%   $30.1319   $30.13   $30.15   $30.10  
  Purchase #7 $157.60   4.809%   $165.179   $165.18   $165.20   $165.20  
  7 purchase totals = $899.75       $991.8689   $991.86   $991.95   $991.80