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	$196.89	13.650%	$223.7655	$223.77	$223.75	$223.80
Purchase #2	$107.27	8.331%	$116.2067	$116.21	$116.20	$116.20
Purchase #3	$106.91	11.443%	$119.1437	$119.14	$119.15	$119.10
Purchase #4	$32.96	8.360%	$35.7155	$35.72	$35.70	$35.70
Purchase #5	$144.59	5.269%	$152.2084	$152.21	$152.20	$152.20
Purchase #6	$40.69	4.536%	$42.5357	$42.54	$42.55	$42.50
Purchase #7	$99.94	9.705%	$109.6392	$109.64	$109.65	$109.60
7 purchase totals =	$729.25		$799.2147	$799.23	$799.20	$799.10