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 $78.99   7.849%   $85.1899   $85.19   $85.20   $85.20  
  Purchase #2 $184.76   8.684%   $200.8046   $200.80   $200.80   $200.80  
  Purchase #3 $219.65   3.407%   $227.1335   $227.13   $227.15   $227.10  
  Purchase #4 $84.54   8.207%   $91.4782   $91.48   $91.50   $91.50  
  Purchase #5 $248.35   5.388%   $261.7311   $261.73   $261.75   $261.70  
  Purchase #6 $205.78   9.617%   $225.5699   $225.57   $225.55   $225.60  
  Purchase #7 $194.28   4.290%   $202.6146   $202.61   $202.60   $202.60  
  7 purchase totals = $1,216.35       $1,294.5218   $1,294.51   $1,294.55   $1,294.50