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 $167.65   10.677%   $185.55   $185.55   $185.55   $185.60  
  Purchase #2 $233.73   9.841%   $256.7314   $256.73   $256.75   $256.70  
  Purchase #3 $39.50   4.796%   $41.3944   $41.39   $41.40   $41.40  
  Purchase #4 $202.53   5.235%   $213.1324   $213.13   $213.15   $213.10  
  Purchase #5 $234.40   13.755%   $266.6417   $266.64   $266.65   $266.60  
  Purchase #6 $118.27   10.407%   $130.5784   $130.58   $130.60   $130.60  
  Purchase #7 $25.91   12.549%   $29.1614   $29.16   $29.15   $29.20  
  7 purchase totals = $1,021.99       $1,123.1897   $1,123.18   $1,123.25   $1,123.20