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 $239.85   8.500%   $260.2373   $260.24   $260.25   $260.20  
  Purchase #2 $215.39   8.615%   $233.9458   $233.95   $233.95   $233.90  
  Purchase #3 $210.40   13.329%   $238.4442   $238.44   $238.45   $238.40  
  Purchase #4 $152.38   13.446%   $172.869   $172.87   $172.85   $172.90  
  Purchase #5 $123.62   9.808%   $135.7446   $135.74   $135.75   $135.70  
  Purchase #6 $159.52   3.667%   $165.3696   $165.37   $165.35   $165.40  
  Purchase #7 $99.93   5.754%   $105.68   $105.68   $105.70   $105.70  
  7 purchase totals = $1,201.09       $1,312.2905   $1,312.29   $1,312.30   $1,312.20