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 $244.88   9.701%   $268.6358   $268.64   $268.65   $268.60  
  Purchase #2 $243.30   8.445%   $263.8467   $263.85   $263.85   $263.80  
  Purchase #3 $118.87   13.780%   $135.2503   $135.25   $135.25   $135.30  
  Purchase #4 $240.79   8.812%   $262.0084   $262.01   $262.00   $262.00  
  Purchase #5 $87.82   5.481%   $92.6334   $92.63   $92.65   $92.60  
  Purchase #6 $95.80   6.510%   $102.0366   $102.04   $102.05   $102.00  
  Purchase #7 $136.93   7.602%   $147.3394   $147.34   $147.35   $147.30  
  7 purchase totals = $1,168.39       $1,271.7506   $1,271.76   $1,271.80   $1,271.60