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 $63.70   5.190%   $67.006   $67.01   $67.00   $67.00  
  Purchase #2 $89.58   7.422%   $96.2286   $96.23   $96.25   $96.20  
  Purchase #3 $243.45   7.596%   $261.9425   $261.94   $261.95   $261.90  
  Purchase #4 $34.79   7.658%   $37.4542   $37.45   $37.45   $37.50  
  Purchase #5 $91.78   10.549%   $101.4619   $101.46   $101.45   $101.50  
  Purchase #6 $10.98   9.261%   $11.9969   $12.00   $12.00   $12.00  
  Purchase #7 $148.63   5.133%   $156.2592   $156.26   $156.25   $156.30  
  7 purchase totals = $682.91       $732.3493   $732.35   $732.35   $732.40