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 $60.78   9.158%   $66.3462   $66.35   $66.35   $66.30  
  Purchase #2 $224.64   10.791%   $248.8809   $248.88   $248.90   $248.90  
  Purchase #3 $64.60   4.443%   $67.4702   $67.47   $67.45   $67.50  
  Purchase #4 $159.43   6.134%   $169.2094   $169.21   $169.20   $169.20  
  Purchase #5 $198.45   10.421%   $219.1305   $219.13   $219.15   $219.10  
  Purchase #6 $244.76   10.262%   $269.8773   $269.88   $269.90   $269.90  
  Purchase #7 $177.51   9.480%   $194.3379   $194.34   $194.35   $194.30  
  7 purchase totals = $1,130.17       $1,235.2524   $1,235.26   $1,235.30   $1,235.20