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 $42.41   5.821%   $44.8787   $44.88   $44.90   $44.90  
  Purchase #2 $25.98   3.658%   $26.9303   $26.93   $26.95   $26.90  
  Purchase #3 $163.71   5.549%   $172.7943   $172.79   $172.80   $172.80  
  Purchase #4 $69.65   3.162%   $71.8523   $71.85   $71.85   $71.90  
  Purchase #5 $71.27   6.769%   $76.0943   $76.09   $76.10   $76.10  
  Purchase #6 $205.37   7.787%   $221.3622   $221.36   $221.35   $221.40  
  Purchase #7 $125.25   5.707%   $132.398   $132.40   $132.40   $132.40  
  7 purchase totals = $703.64       $746.3101   $746.30   $746.35   $746.40