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	$36.66	3.167%	$37.821	$37.82	$37.80	$37.80
Purchase #2	$189.58	6.583%	$202.0601	$202.06	$202.05	$202.10
Purchase #3	$116.46	5.715%	$123.1157	$123.12	$123.10	$123.10
Purchase #4	$224.83	11.407%	$250.4764	$250.48	$250.50	$250.50
Purchase #5	$223.76	9.612%	$245.2678	$245.27	$245.25	$245.30
Purchase #6	$211.55	8.659%	$229.8681	$229.87	$229.85	$229.90
Purchase #7	$74.64	11.486%	$83.2132	$83.21	$83.20	$83.20
7 purchase totals =	$1,077.48		$1,171.8223	$1,171.83	$1,171.75	$1,171.90