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 $230.48   10.599%   $254.9086   $254.91   $254.90   $254.90  
  Purchase #2 $248.51   5.849%   $263.0453   $263.05   $263.05   $263.00  
  Purchase #3 $59.62   10.499%   $65.8795   $65.88   $65.90   $65.90  
  Purchase #4 $212.38   3.292%   $219.3715   $219.37   $219.35   $219.40  
  Purchase #5 $92.28   9.865%   $101.3834   $101.38   $101.40   $101.40  
  Purchase #6 $237.36   12.322%   $266.6075   $266.61   $266.60   $266.60  
  Purchase #7 $183.29   11.595%   $204.5425   $204.54   $204.55   $204.50  
  7 purchase totals = $1,263.92       $1,375.7383   $1,375.74   $1,375.75   $1,375.70