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 $90.86   8.489%   $98.5731   $98.57   $98.55   $98.60  
  Purchase #2 $84.49   5.132%   $88.826   $88.83   $88.85   $88.80  
  Purchase #3 $49.46   9.396%   $54.1073   $54.11   $54.10   $54.10  
  Purchase #4 $123.44   7.693%   $132.9362   $132.94   $132.95   $132.90  
  Purchase #5 $200.71   12.673%   $226.146   $226.15   $226.15   $226.10  
  Purchase #6 $135.75   12.243%   $152.3699   $152.37   $152.35   $152.40  
  Purchase #7 $47.62   5.626%   $50.2991   $50.30   $50.30   $50.30  
  7 purchase totals = $732.33       $803.2576   $803.27   $803.25   $803.20