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 $68.75   9.130%   $75.0269   $75.03   $75.05   $75.00  
  Purchase #2 $29.91   6.472%   $31.8458   $31.85   $31.85   $31.80  
  Purchase #3 $98.86   6.772%   $105.5548   $105.55   $105.55   $105.60  
  Purchase #4 $214.84   6.727%   $229.2923   $229.29   $229.30   $229.30  
  Purchase #5 $104.30   3.301%   $107.7429   $107.74   $107.75   $107.70  
  Purchase #6 $124.63   3.760%   $129.3161   $129.32   $129.30   $129.30  
  Purchase #7 $81.30   13.819%   $92.5348   $92.53   $92.55   $92.50  
  7 purchase totals = $722.59       $771.3136   $771.31   $771.35   $771.20