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 $49.81   11.127%   $55.3524   $55.35   $55.35   $55.40  
  Purchase #2 $46.51   5.475%   $49.0564   $49.06   $49.05   $49.10  
  Purchase #3 $124.31   3.284%   $128.3923   $128.39   $128.40   $128.40  
  Purchase #4 $27.32   8.842%   $29.7356   $29.74   $29.75   $29.70  
  Purchase #5 $216.60   11.604%   $241.7343   $241.73   $241.75   $241.70  
  Purchase #6 $93.92   5.727%   $99.2988   $99.30   $99.30   $99.30  
  Purchase #7 $65.98   11.220%   $73.383   $73.38   $73.40   $73.40  
  7 purchase totals = $624.45       $676.9528   $676.95   $677.00   $677.00