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 $60.65   13.252%   $68.6873   $68.69   $68.70   $68.70  
  Purchase #2 $71.67   9.271%   $78.3145   $78.31   $78.30   $78.30  
  Purchase #3 $156.80   5.520%   $165.4554   $165.46   $165.45   $165.50  
  Purchase #4 $230.87   4.818%   $241.9933   $241.99   $242.00   $242.00  
  Purchase #5 $74.77   10.473%   $82.6007   $82.60   $82.60   $82.60  
  Purchase #6 $5.73   9.744%   $6.2883   $6.29   $6.30   $6.30  
  Purchase #7 $53.96   12.203%   $60.5447   $60.54   $60.55   $60.50  
  7 purchase totals = $654.45       $703.8842   $703.88   $703.90   $703.90