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 $174.68   6.639%   $186.277   $186.28   $186.30   $186.30  
  Purchase #2 $187.40   6.159%   $198.942   $198.94   $198.95   $198.90  
  Purchase #3 $91.39   6.741%   $97.5506   $97.55   $97.55   $97.60  
  Purchase #4 $181.34   4.548%   $189.5873   $189.59   $189.60   $189.60  
  Purchase #5 $110.33   5.292%   $116.1687   $116.17   $116.15   $116.20  
  Purchase #6 $152.61   8.774%   $166   $166.00   $166.00   $166.00  
  Purchase #7 $26.39   3.408%   $27.2894   $27.29   $27.30   $27.30  
  7 purchase totals = $924.14       $981.8150   $981.82   $981.85   $981.90