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 $184.59   12.653%   $207.9462   $207.95   $207.95   $207.90  
  Purchase #2 $190.25   4.746%   $199.2793   $199.28   $199.30   $199.30  
  Purchase #3 $114.82   3.642%   $119.0017   $119.00   $119.00   $119.00  
  Purchase #4 $59.81   11.260%   $66.5446   $66.54   $66.55   $66.50  
  Purchase #5 $86.94   8.571%   $94.3916   $94.39   $94.40   $94.40  
  Purchase #6 $15.36   13.445%   $17.4252   $17.43   $17.45   $17.40  
  Purchase #7 $26.95   10.199%   $29.6986   $29.70   $29.70   $29.70  
  7 purchase totals = $678.72       $734.2872   $734.29   $734.35   $734.20