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	$242.99	12.363%	$273.0309	$273.03	$273.05	$273.00
Purchase #2	$215.74	11.700%	$240.9816	$240.98	$241.00	$241.00
Purchase #3	$114.61	13.696%	$130.307	$130.31	$130.30	$130.30
Purchase #4	$130.56	6.151%	$138.5907	$138.59	$138.60	$138.60
Purchase #5	$149.91	6.705%	$159.9615	$159.96	$159.95	$160.00
Purchase #6	$55.36	4.507%	$57.8551	$57.86	$57.85	$57.90
Purchase #7	$43.73	3.227%	$45.1412	$45.14	$45.15	$45.10
7 purchase totals =	$952.90		$1,045.8680	$1,045.87	$1,045.90	$1,045.90