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 $11.52   3.468%   $11.9195   $11.92   $11.90   $11.90  
  Purchase #2 $116.34   6.691%   $124.1243   $124.12   $124.10   $124.10  
  Purchase #3 $126.66   3.367%   $130.9246   $130.92   $130.90   $130.90  
  Purchase #4 $141.84   13.862%   $161.5019   $161.50   $161.50   $161.50  
  Purchase #5 $130.99   7.205%   $140.4278   $140.43   $140.45   $140.40  
  Purchase #6 $73.45   4.599%   $76.828   $76.83   $76.85   $76.80  
  Purchase #7 $126.93   5.570%   $134   $134.00   $134.00   $134.00  
  7 purchase totals = $727.73       $779.7261   $779.72   $779.70   $779.60