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	$171.36	8.834%	$186.4979	$186.50	$186.50	$186.50
Purchase #2	$99.33	12.467%	$111.7135	$111.71	$111.70	$111.70
Purchase #3	$58.57	3.402%	$60.5626	$60.56	$60.55	$60.60
Purchase #4	$70.92	9.830%	$77.8914	$77.89	$77.90	$77.90
Purchase #5	$18.25	3.349%	$18.8612	$18.86	$18.85	$18.90
Purchase #6	$144.36	13.753%	$164.2138	$164.21	$164.20	$164.20
Purchase #7	$191.84	13.492%	$217.7231	$217.72	$217.70	$217.70
7 purchase totals =	$754.63		$837.4635	$837.45	$837.40	$837.50