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 $122.94   9.204%   $134.2554   $134.26   $134.25   $134.30  
  Purchase #2 $242.79   7.664%   $261.3974   $261.40   $261.40   $261.40  
  Purchase #3 $235.80   11.826%   $263.6857   $263.69   $263.70   $263.70  
  Purchase #4 $119.29   4.585%   $124.7594   $124.76   $124.75   $124.80  
  Purchase #5 $205.25   13.844%   $233.6648   $233.66   $233.65   $233.70  
  Purchase #6 $115.52   4.182%   $120.351   $120.35   $120.35   $120.40  
  Purchase #7 $152.55   7.192%   $163.5214   $163.52   $163.50   $163.50  
  7 purchase totals = $1,194.14       $1,301.6351   $1,301.64   $1,301.60   $1,301.80