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 $63.96   8.362%   $69.3083   $69.31   $69.30   $69.30  
  Purchase #2 $245.65   6.153%   $260.7648   $260.76   $260.75   $260.80  
  Purchase #3 $41.52   5.286%   $43.7147   $43.71   $43.70   $43.70  
  Purchase #4 $208.39   12.266%   $233.9511   $233.95   $233.95   $234.00  
  Purchase #5 $195.46   11.780%   $218.4852   $218.49   $218.50   $218.50  
  Purchase #6 $249.51   9.370%   $272.8891   $272.89   $272.90   $272.90  
  Purchase #7 $95.74   3.852%   $99.4279   $99.43   $99.45   $99.40  
  7 purchase totals = $1,100.23       $1,198.5411   $1,198.54   $1,198.55   $1,198.60