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	$25.35	13.732%	$28.8311	$28.83	$28.85	$28.80
Purchase #2	$147.72	11.765%	$165.0993	$165.10	$165.10	$165.10
Purchase #3	$54.56	8.550%	$59.2249	$59.22	$59.20	$59.20
Purchase #4	$114.53	8.208%	$123.9306	$123.93	$123.95	$123.90
Purchase #5	$51.54	13.174%	$58.3299	$58.33	$58.35	$58.30
Purchase #6	$70.61	8.857%	$76.8639	$76.86	$76.85	$76.90
Purchase #7	$23.43	4.380%	$24.4562	$24.46	$24.45	$24.50
7 purchase totals =	$487.74		$536.7359	$536.73	$536.75	$536.70