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 $191.43   8.340%   $207.3953   $207.40   $207.40   $207.40  
  Purchase #2 $166.94   9.851%   $183.3853   $183.39   $183.40   $183.40  
  Purchase #3 $137.70   11.560%   $153.6181   $153.62   $153.60   $153.60  
  Purchase #4 $169.77   9.510%   $185.9151   $185.92   $185.90   $185.90  
  Purchase #5 $237.80   12.164%   $266.726   $266.73   $266.75   $266.70  
  Purchase #6 $157.44   8.136%   $170.2493   $170.25   $170.25   $170.20  
  Purchase #7 $54.97   7.434%   $59.0565   $59.06   $59.05   $59.10  
  7 purchase totals = $1,116.05       $1,226.3456   $1,226.37   $1,226.35   $1,226.30