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 $60.83   11.816%   $68.0177   $68.02   $68.00   $68.00  
  Purchase #2 $237.47   13.342%   $269.1532   $269.15   $269.15   $269.20  
  Purchase #3 $139.72   4.313%   $145.7461   $145.75   $145.75   $145.70  
  Purchase #4 $56.29   12.867%   $63.5328   $63.53   $63.55   $63.50  
  Purchase #5 $219.61   11.392%   $244.628   $244.63   $244.65   $244.60  
  Purchase #6 $213.40   4.311%   $222.5997   $222.60   $222.60   $222.60  
  Purchase #7 $188.98   5.737%   $199.8218   $199.82   $199.80   $199.80  
  7 purchase totals = $1,116.30       $1,213.4993   $1,213.50   $1,213.50   $1,213.40