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	$158.33	4.632%	$165.6638	$165.66	$165.65	$165.70
Purchase #2	$99.96	7.275%	$107.2321	$107.23	$107.25	$107.20
Purchase #3	$162.33	3.511%	$168.0294	$168.03	$168.05	$168.00
Purchase #4	$184.72	13.205%	$209.1123	$209.11	$209.10	$209.10
Purchase #5	$33.57	8.232%	$36.3335	$36.33	$36.35	$36.30
Purchase #6	$200.63	11.860%	$224.4247	$224.42	$224.40	$224.40
Purchase #7	$69.40	4.208%	$72.3204	$72.32	$72.30	$72.30
7 purchase totals =	$908.94		$983.1162	$983.10	$983.10	$983.00