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 $169.88   8.424%   $184.1907   $184.19   $184.20   $184.20  
  Purchase #2 $118.62   6.647%   $126.5047   $126.50   $126.50   $126.50  
  Purchase #3 $236.37   5.723%   $249.8975   $249.90   $249.90   $249.90  
  Purchase #4 $14.47   13.313%   $16.3964   $16.40   $16.40   $16.40  
  Purchase #5 $145.44   5.386%   $153.2734   $153.27   $153.25   $153.30  
  Purchase #6 $53.89   6.763%   $57.5346   $57.53   $57.55   $57.50  
  Purchase #7 $221.87   6.298%   $235.8434   $235.84   $235.85   $235.80  
  7 purchase totals = $960.54       $1,023.6407   $1,023.63   $1,023.65   $1,023.60