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 $240.98   11.628%   $269.0012   $269.00   $269.00   $269.00  
  Purchase #2 $168.95   4.324%   $176.2554   $176.26   $176.25   $176.30  
  Purchase #3 $177.42   9.710%   $194.6475   $194.65   $194.65   $194.60  
  Purchase #4 $9.31   9.551%   $10.1992   $10.20   $10.20   $10.20  
  Purchase #5 $34.51   8.119%   $37.3119   $37.31   $37.30   $37.30  
  Purchase #6 $115.47   4.475%   $120.6373   $120.64   $120.65   $120.60  
  Purchase #7 $23.37   11.265%   $26.0026   $26.00   $26.00   $26.00  
  7 purchase totals = $770.01       $834.0551   $834.06   $834.05   $834.00