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	$174.31	3.585%	$180.559	$180.56	$180.55	$180.60
Purchase #2	$126.47	10.720%	$140.0276	$140.03	$140.05	$140.00
Purchase #3	$91.44	8.729%	$99.4218	$99.42	$99.40	$99.40
Purchase #4	$7.26	8.672%	$7.8896	$7.89	$7.90	$7.90
Purchase #5	$139.26	11.753%	$155.6272	$155.63	$155.65	$155.60
Purchase #6	$162.66	5.335%	$171.3379	$171.34	$171.35	$171.30
Purchase #7	$59.49	8.449%	$64.5163	$64.52	$64.50	$64.50
7 purchase totals =	$760.89		$819.3794	$819.39	$819.40	$819.30