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 $244.93   10.790%   $271.3579   $271.36   $271.35   $271.40  
  Purchase #2 $92.59   5.298%   $97.4954   $97.50   $97.50   $97.50  
  Purchase #3 $56.26   3.302%   $58.1177   $58.12   $58.10   $58.10  
  Purchase #4 $167.49   6.777%   $178.8408   $178.84   $178.85   $178.80  
  Purchase #5 $106.77   7.465%   $114.7404   $114.74   $114.75   $114.70  
  Purchase #6 $122.37   10.247%   $134.9093   $134.91   $134.90   $134.90  
  Purchase #7 $159.52   11.519%   $177.8951   $177.90   $177.90   $177.90  
  7 purchase totals = $949.93       $1,033.3566   $1,033.37   $1,033.35   $1,033.30