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 $237.84   11.694%   $265.653   $265.65   $265.65   $265.70  
  Purchase #2 $96.48   7.557%   $103.771   $103.77   $103.75   $103.80  
  Purchase #3 $197.64   9.759%   $216.9277   $216.93   $216.95   $216.90  
  Purchase #4 $178.64   8.307%   $193.4796   $193.48   $193.50   $193.50  
  Purchase #5 $67.54   11.178%   $75.0896   $75.09   $75.10   $75.10  
  Purchase #6 $248.95   4.574%   $260.337   $260.34   $260.35   $260.30  
  Purchase #7 $207.34   13.638%   $235.617   $235.62   $235.60   $235.60  
  7 purchase totals = $1,234.43       $1,350.8749   $1,350.88   $1,350.90   $1,350.90