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 $90.49   5.655%   $95.6072   $95.61   $95.60   $95.60  
  Purchase #2 $244.33   12.746%   $275.4723   $275.47   $275.45   $275.50  
  Purchase #3 $193.40   11.405%   $215.4573   $215.46   $215.45   $215.50  
  Purchase #4 $22.74   8.598%   $24.6952   $24.70   $24.70   $24.70  
  Purchase #5 $237.62   8.853%   $258.6565   $258.66   $258.65   $258.70  
  Purchase #6 $79.72   8.339%   $86.3679   $86.37   $86.35   $86.40  
  Purchase #7 $51.43   12.401%   $57.8078   $57.81   $57.80   $57.80  
  7 purchase totals = $919.73       $1,014.0642   $1,014.08   $1,014.00   $1,014.20