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 $214.82   6.387%   $228.5406   $228.54   $228.55   $228.50  
  Purchase #2 $63.47   4.507%   $66.3306   $66.33   $66.35   $66.30  
  Purchase #3 $110.32   4.471%   $115.2524   $115.25   $115.25   $115.30  
  Purchase #4 $53.27   7.644%   $57.342   $57.34   $57.35   $57.30  
  Purchase #5 $36.28   4.728%   $37.9953   $38.00   $38.00   $38.00  
  Purchase #6 $110.84   3.411%   $114.6208   $114.62   $114.60   $114.60  
  Purchase #7 $80.73   5.554%   $85.2137   $85.21   $85.20   $85.20  
  7 purchase totals = $669.73       $705.2954   $705.29   $705.30   $705.20