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	$65.58	12.786%	$73.9651	$73.97	$73.95	$74.00
Purchase #2	$125.89	10.533%	$139.15	$139.15	$139.15	$139.20
Purchase #3	$45.69	6.818%	$48.8051	$48.81	$48.80	$48.80
Purchase #4	$99.91	4.371%	$104.2771	$104.28	$104.30	$104.30
Purchase #5	$47.42	9.333%	$51.8457	$51.85	$51.85	$51.80
Purchase #6	$213.76	13.391%	$242.3846	$242.38	$242.40	$242.40
Purchase #7	$83.48	7.111%	$89.4163	$89.42	$89.40	$89.40
7 purchase totals =	$681.73		$749.8439	$749.86	$749.85	$749.90