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	$155.31	12.125%	$174.1413	$174.14	$174.15	$174.10
Purchase #2	$52.44	10.152%	$57.7637	$57.76	$57.75	$57.80
Purchase #3	$166.73	13.117%	$188.6	$188.60	$188.60	$188.60
Purchase #4	$124.42	12.437%	$139.8941	$139.89	$139.90	$139.90
Purchase #5	$161.34	6.740%	$172.2143	$172.21	$172.20	$172.20
Purchase #6	$80.40	9.576%	$88.0991	$88.10	$88.10	$88.10
Purchase #7	$159.91	7.440%	$171.8073	$171.81	$171.80	$171.80
7 purchase totals =	$900.55		$992.5198	$992.51	$992.50	$992.50