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 $67.27   12.433%   $75.6337   $75.63   $75.65   $75.60  
  Purchase #2 $56.97   5.363%   $60.0253   $60.03   $60.05   $60.00  
  Purchase #3 $113.97   4.637%   $119.2548   $119.25   $119.25   $119.30  
  Purchase #4 $113.29   8.119%   $122.488   $122.49   $122.50   $122.50  
  Purchase #5 $94.27   4.415%   $98.432   $98.43   $98.45   $98.40  
  Purchase #6 $88.74   6.652%   $94.643   $94.64   $94.65   $94.60  
  Purchase #7 $163.57   11.576%   $182.5049   $182.50   $182.50   $182.50  
  7 purchase totals = $698.08       $752.9817   $752.97   $753.05   $752.90