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 $104.49   10.559%   $115.5231   $115.52   $115.50   $115.50  
  Purchase #2 $223.42   11.131%   $248.2889   $248.29   $248.30   $248.30  
  Purchase #3 $92.51   9.843%   $101.6158   $101.62   $101.60   $101.60  
  Purchase #4 $55.77   7.678%   $60.052   $60.05   $60.05   $60.10  
  Purchase #5 $28.80   6.422%   $30.6495   $30.65   $30.65   $30.60  
  Purchase #6 $98.95   7.771%   $106.6394   $106.64   $106.65   $106.60  
  Purchase #7 $240.52   4.315%   $250.8984   $250.90   $250.90   $250.90  
  7 purchase totals = $844.46       $913.6671   $913.67   $913.65   $913.60