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	$31.34	10.822%	$34.7316	$34.73	$34.75	$34.70
Purchase #2	$146.40	13.222%	$165.757	$165.76	$165.75	$165.80
Purchase #3	$170.54	11.155%	$189.5637	$189.56	$189.55	$189.60
Purchase #4	$35.74	11.663%	$39.9084	$39.91	$39.90	$39.90
Purchase #5	$106.25	11.408%	$118.371	$118.37	$118.35	$118.40
Purchase #6	$36.78	4.214%	$38.3299	$38.33	$38.35	$38.30
Purchase #7	$144.50	11.313%	$160.8473	$160.85	$160.85	$160.80
7 purchase totals =	$671.55		$747.5089	$747.51	$747.50	$747.50