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	$189.62	10.362%	$209.2684	$209.27	$209.25	$209.30
Purchase #2	$26.37	12.732%	$29.7274	$29.73	$29.75	$29.70
Purchase #3	$121.55	8.326%	$131.6703	$131.67	$131.65	$131.70
Purchase #4	$80.43	10.805%	$89.1205	$89.12	$89.10	$89.10
Purchase #5	$152.38	12.362%	$171.2172	$171.22	$171.20	$171.20
Purchase #6	$240.39	4.107%	$250.2628	$250.26	$250.25	$250.30
Purchase #7	$197.32	11.123%	$219.2679	$219.27	$219.25	$219.30
7 purchase totals =	$1,008.06		$1,100.5345	$1,100.54	$1,100.45	$1,100.60