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	$69.34	3.160%	$71.5311	$71.53	$71.55	$71.50
Purchase #2	$123.28	13.452%	$139.8636	$139.86	$139.85	$139.90
Purchase #3	$162.97	8.334%	$176.5519	$176.55	$176.55	$176.60
Purchase #4	$143.89	9.744%	$157.9106	$157.91	$157.90	$157.90
Purchase #5	$38.79	8.523%	$42.0961	$42.10	$42.10	$42.10
Purchase #6	$13.25	4.477%	$13.8432	$13.84	$13.85	$13.80
Purchase #7	$85.44	7.871%	$92.165	$92.17	$92.15	$92.20
7 purchase totals =	$636.96		$693.9615	$693.96	$693.95	$694.00