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 $246.99   12.234%   $277.2068   $277.21   $277.20   $277.20  
  Purchase #2 $212.67   11.498%   $237.1228   $237.12   $237.10   $237.10  
  Purchase #3 $92.72   4.686%   $97.0649   $97.06   $97.05   $97.10  
  Purchase #4 $199.59   3.409%   $206.394   $206.39   $206.40   $206.40  
  Purchase #5 $183.67   5.864%   $194.4404   $194.44   $194.45   $194.40  
  Purchase #6 $169.30   4.158%   $176.3395   $176.34   $176.35   $176.30  
  Purchase #7 $210.72   4.285%   $219.7494   $219.75   $219.75   $219.70  
  7 purchase totals = $1,315.66       $1,408.3178   $1,408.31   $1,408.30   $1,408.20