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 $60.74   11.316%   $67.6133   $67.61   $67.60   $67.60  
  Purchase #2 $244.45   5.814%   $258.6623   $258.66   $258.65   $258.70  
  Purchase #3 $146.49   9.544%   $160.471   $160.47   $160.45   $160.50  
  Purchase #4 $60.31   9.428%   $65.996   $66.00   $66.00   $66.00  
  Purchase #5 $171.28   9.664%   $187.8325   $187.83   $187.85   $187.80  
  Purchase #6 $156.99   5.115%   $165.02   $165.02   $165.00   $165.00  
  Purchase #7 $60.63   11.336%   $67.503   $67.50   $67.50   $67.50  
  7 purchase totals = $900.89       $973.0981   $973.09   $973.05   $973.10