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 $180.34   8.138%   $195.0161   $195.02   $195.00   $195.00  
  Purchase #2 $51.93   13.334%   $58.8543   $58.85   $58.85   $58.90  
  Purchase #3 $153.74   13.339%   $174.2474   $174.25   $174.25   $174.20  
  Purchase #4 $106.62   8.494%   $115.6763   $115.68   $115.70   $115.70  
  Purchase #5 $234.33   3.328%   $242.1285   $242.13   $242.15   $242.10  
  Purchase #6 $229.50   9.511%   $251.3277   $251.33   $251.35   $251.30  
  Purchase #7 $70.67   7.533%   $75.9936   $75.99   $76.00   $76.00  
  7 purchase totals = $1,027.13       $1,113.2439   $1,113.25   $1,113.30   $1,113.20