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 $223.61   8.237%   $242.0288   $242.03   $242.05   $242.00  
  Purchase #2 $100.91   6.103%   $107.0685   $107.07   $107.05   $107.10  
  Purchase #3 $184.34   5.341%   $194.1856   $194.19   $194.20   $194.20  
  Purchase #4 $219.97   11.202%   $244.611   $244.61   $244.60   $244.60  
  Purchase #5 $65.34   4.592%   $68.3404   $68.34   $68.35   $68.30  
  Purchase #6 $61.40   10.282%   $67.7131   $67.71   $67.70   $67.70  
  Purchase #7 $84.72   7.496%   $91.0706   $91.07   $91.05   $91.10  
  7 purchase totals = $940.29       $1,015.0180   $1,015.02   $1,015.00   $1,015.00