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 $161.32   13.376%   $182.8982   $182.90   $182.90   $182.90  
  Purchase #2 $34.95   9.712%   $38.3443   $38.34   $38.35   $38.30  
  Purchase #3 $97.45   4.857%   $102.1831   $102.18   $102.20   $102.20  
  Purchase #4 $192.39   4.832%   $201.6863   $201.69   $201.70   $201.70  
  Purchase #5 $15.28   8.286%   $16.5461   $16.55   $16.55   $16.50  
  Purchase #6 $149.40   8.701%   $162.3993   $162.40   $162.40   $162.40  
  Purchase #7 $55.86   11.313%   $62.1794   $62.18   $62.20   $62.20  
  7 purchase totals = $706.65       $766.2367   $766.24   $766.30   $766.20