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 $68.58   12.162%   $76.9207   $76.92   $76.90   $76.90  
  Purchase #2 $51.82   7.703%   $55.8117   $55.81   $55.80   $55.80  
  Purchase #3 $37.45   8.188%   $40.5164   $40.52   $40.50   $40.50  
  Purchase #4 $94.53   13.229%   $107.0354   $107.04   $107.05   $107.00  
  Purchase #5 $246.88   8.187%   $267.0921   $267.09   $267.10   $267.10  
  Purchase #6 $144.39   13.600%   $164.027   $164.03   $164.05   $164.00  
  Purchase #7 $171.80   9.354%   $187.8702   $187.87   $187.85   $187.90  
  7 purchase totals = $815.45       $899.2735   $899.28   $899.25   $899.20