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 $206.46   10.124%   $227.362   $227.36   $227.35   $227.40  
  Purchase #2 $250.39   10.615%   $276.9689   $276.97   $276.95   $277.00  
  Purchase #3 $77.37   6.113%   $82.0996   $82.10   $82.10   $82.10  
  Purchase #4 $250.52   4.782%   $262.4999   $262.50   $262.50   $262.50  
  Purchase #5 $49.26   13.728%   $56.0224   $56.02   $56.00   $56.00  
  Purchase #6 $123.68   10.268%   $136.3795   $136.38   $136.40   $136.40  
  Purchase #7 $199.90   5.854%   $211.6021   $211.60   $211.60   $211.60  
  7 purchase totals = $1,157.58       $1,252.9344   $1,252.93   $1,252.90   $1,253.00