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 $59.92   11.798%   $66.9894   $66.99   $67.00   $67.00  
  Purchase #2 $194.95   9.495%   $213.4605   $213.46   $213.45   $213.50  
  Purchase #3 $232.96   3.822%   $241.8637   $241.86   $241.85   $241.90  
  Purchase #4 $16.28   6.129%   $17.2778   $17.28   $17.30   $17.30  
  Purchase #5 $93.40   9.490%   $102.2637   $102.26   $102.25   $102.30  
  Purchase #6 $95.56   12.705%   $107.7009   $107.70   $107.70   $107.70  
  Purchase #7 $178.25   11.113%   $198.0589   $198.06   $198.05   $198.10  
  7 purchase totals = $871.32       $947.6149   $947.61   $947.60   $947.80