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 $182.34   6.557%   $194.296   $194.30   $194.30   $194.30  
  Purchase #2 $59.43   7.315%   $63.7773   $63.78   $63.80   $63.80  
  Purchase #3 $187.84   13.257%   $212.7419   $212.74   $212.75   $212.70  
  Purchase #4 $207.30   12.832%   $233.9007   $233.90   $233.90   $233.90  
  Purchase #5 $24.67   5.431%   $26.0098   $26.01   $26.00   $26.00  
  Purchase #6 $23.63   3.797%   $24.5272   $24.53   $24.55   $24.50  
  Purchase #7 $19.37   7.204%   $20.7654   $20.77   $20.75   $20.80  
  7 purchase totals = $704.58       $776.0183   $776.03   $776.05   $776.00