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 $60.41   8.108%   $65.308   $65.31   $65.30   $65.30  
  Purchase #2 $195.89   8.602%   $212.7405   $212.74   $212.75   $212.70  
  Purchase #3 $122.37   7.502%   $131.5502   $131.55   $131.55   $131.60  
  Purchase #4 $182.33   6.448%   $194.0866   $194.09   $194.10   $194.10  
  Purchase #5 $198.90   13.419%   $225.5904   $225.59   $225.60   $225.60  
  Purchase #6 $5.31   6.201%   $5.6393   $5.64   $5.65   $5.60  
  Purchase #7 $143.25   13.335%   $162.3524   $162.35   $162.35   $162.40  
  7 purchase totals = $908.46       $997.2674   $997.27   $997.30   $997.30