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 $208.86   9.130%   $227.9289   $227.93   $227.95   $227.90  
  Purchase #2 $120.98   5.319%   $127.4149   $127.41   $127.40   $127.40  
  Purchase #3 $23.45   5.405%   $24.7175   $24.72   $24.70   $24.70  
  Purchase #4 $109.82   9.357%   $120.0959   $120.10   $120.10   $120.10  
  Purchase #5 $249.66   5.394%   $263.1267   $263.13   $263.15   $263.10  
  Purchase #6 $136.67   4.364%   $142.6343   $142.63   $142.65   $142.60  
  Purchase #7 $115.93   9.156%   $126.5446   $126.54   $126.55   $126.50  
  7 purchase totals = $965.37       $1,032.4628   $1,032.46   $1,032.50   $1,032.30