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	$247.78	10.266%	$273.2171	$273.22	$273.20	$273.20
Purchase #2	$7.74	9.338%	$8.4628	$8.46	$8.45	$8.50
Purchase #3	$148.82	7.297%	$159.6794	$159.68	$159.70	$159.70
Purchase #4	$50.27	13.498%	$57.0554	$57.06	$57.05	$57.10
Purchase #5	$120.94	8.338%	$131.024	$131.02	$131.00	$131.00
Purchase #6	$104.80	6.764%	$111.8887	$111.89	$111.90	$111.90
Purchase #7	$224.61	3.353%	$232.1412	$232.14	$232.15	$232.10
7 purchase totals =	$904.96		$973.4686	$973.47	$973.45	$973.50