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 $54.40   9.593%   $59.6186   $59.62   $59.60   $59.60  
  Purchase #2 $77.40   9.459%   $84.7213   $84.72   $84.70   $84.70  
  Purchase #3 $220.26   12.468%   $247.722   $247.72   $247.70   $247.70  
  Purchase #4 $197.69   13.489%   $224.3564   $224.36   $224.35   $224.40  
  Purchase #5 $159.69   9.149%   $174.3   $174.30   $174.30   $174.30  
  Purchase #6 $85.88   11.334%   $95.6136   $95.61   $95.60   $95.60  
  Purchase #7 $190.53   5.734%   $201.455   $201.46   $201.45   $201.50  
  7 purchase totals = $985.85       $1,087.7869   $1,087.79   $1,087.70   $1,087.80