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 $44.41   9.357%   $48.5654   $48.57   $48.55   $48.60  
  Purchase #2 $167.86   11.711%   $187.5181   $187.52   $187.50   $187.50  
  Purchase #3 $24.36   6.278%   $25.8893   $25.89   $25.90   $25.90  
  Purchase #4 $17.31   4.291%   $18.0528   $18.05   $18.05   $18.10  
  Purchase #5 $207.96   12.125%   $233.1752   $233.18   $233.20   $233.20  
  Purchase #6 $190.65   12.431%   $214.3497   $214.35   $214.35   $214.30  
  Purchase #7 $164.73   9.254%   $179.9741   $179.97   $179.95   $180.00  
  7 purchase totals = $817.28       $907.5246   $907.53   $907.50   $907.60