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 $233.90   12.285%   $262.6346   $262.63   $262.65   $262.60  
  Purchase #2 $54.66   9.373%   $59.7833   $59.78   $59.80   $59.80  
  Purchase #3 $58.44   6.605%   $62.3   $62.30   $62.30   $62.30  
  Purchase #4 $18.88   11.516%   $21.0542   $21.05   $21.05   $21.10  
  Purchase #5 $101.98   5.194%   $107.2768   $107.28   $107.30   $107.30  
  Purchase #6 $219.62   8.387%   $238.0395   $238.04   $238.05   $238.00  
  Purchase #7 $153.59   10.173%   $169.2147   $169.21   $169.20   $169.20  
  7 purchase totals = $841.07       $920.3031   $920.29   $920.35   $920.30