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 $243.49   13.823%   $277.1476   $277.15   $277.15   $277.10  
  Purchase #2 $167.36   13.720%   $190.3218   $190.32   $190.30   $190.30  
  Purchase #3 $215.92   5.474%   $227.7395   $227.74   $227.75   $227.70  
  Purchase #4 $90.54   4.399%   $94.5229   $94.52   $94.50   $94.50  
  Purchase #5 $46.89   10.459%   $51.7942   $51.79   $51.80   $51.80  
  Purchase #6 $166.25   3.230%   $171.6199   $171.62   $171.60   $171.60  
  Purchase #7 $83.55   9.158%   $91.2015   $91.20   $91.20   $91.20  
  7 purchase totals = $1,014.00       $1,104.3474   $1,104.34   $1,104.30   $1,104.20