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 $98.52   5.813%   $104.247   $104.25   $104.25   $104.20  
  Purchase #2 $112.98   13.802%   $128.5735   $128.57   $128.55   $128.60  
  Purchase #3 $57.91   3.353%   $59.8517   $59.85   $59.85   $59.90  
  Purchase #4 $190.43   12.180%   $213.6244   $213.62   $213.60   $213.60  
  Purchase #5 $194.49   12.711%   $219.2116   $219.21   $219.20   $219.20  
  Purchase #6 $75.31   12.801%   $84.9504   $84.95   $84.95   $85.00  
  Purchase #7 $200.29   3.232%   $206.7634   $206.76   $206.75   $206.80  
  7 purchase totals = $929.93       $1,017.2220   $1,017.21   $1,017.15   $1,017.30