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 $41.73   11.145%   $46.3808   $46.38   $46.40   $46.40  
  Purchase #2 $17.97   12.802%   $20.2705   $20.27   $20.25   $20.30  
  Purchase #3 $113.68   10.687%   $125.829   $125.83   $125.85   $125.80  
  Purchase #4 $178.30   5.601%   $188.2866   $188.29   $188.30   $188.30  
  Purchase #5 $68.25   13.274%   $77.3095   $77.31   $77.30   $77.30  
  Purchase #6 $56.74   6.810%   $60.604   $60.60   $60.60   $60.60  
  Purchase #7 $178.76   10.187%   $196.9703   $196.97   $196.95   $197.00  
  7 purchase totals = $655.43       $715.6507   $715.65   $715.65   $715.70