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 $97.93   12.632%   $110.3005   $110.30   $110.30   $110.30  
  Purchase #2 $166.88   13.465%   $189.3504   $189.35   $189.35   $189.40  
  Purchase #3 $49.66   13.353%   $56.2911   $56.29   $56.30   $56.30  
  Purchase #4 $32.30   11.316%   $35.9551   $35.96   $35.95   $36.00  
  Purchase #5 $162.68   8.171%   $175.9726   $175.97   $175.95   $176.00  
  Purchase #6 $54.29   7.244%   $58.2228   $58.22   $58.20   $58.20  
  Purchase #7 $115.95   12.251%   $130.155   $130.16   $130.15   $130.20  
  7 purchase totals = $679.69       $756.2475   $756.25   $756.20   $756.40