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 $231.94   9.466%   $253.8954   $253.90   $253.90   $253.90  
  Purchase #2 $54.83   8.579%   $59.5339   $59.53   $59.55   $59.50  
  Purchase #3 $25.94   3.182%   $26.7654   $26.77   $26.75   $26.80  
  Purchase #4 $75.75   5.398%   $79.839   $79.84   $79.85   $79.80  
  Purchase #5 $219.66   4.385%   $229.2921   $229.29   $229.30   $229.30  
  Purchase #6 $149.78   3.481%   $154.9938   $154.99   $155.00   $155.00  
  Purchase #7 $195.79   11.493%   $218.2921   $218.29   $218.30   $218.30  
  7 purchase totals = $953.69       $1,022.6117   $1,022.61   $1,022.65   $1,022.60