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	$216.91	6.533%	$231.0807	$231.08	$231.10	$231.10
Purchase #2	$152.58	8.253%	$165.1724	$165.17	$165.15	$165.20
Purchase #3	$242.33	12.311%	$272.1632	$272.16	$272.15	$272.20
Purchase #4	$30.37	3.279%	$31.3658	$31.37	$31.35	$31.40
Purchase #5	$149.62	11.254%	$166.4582	$166.46	$166.45	$166.50
Purchase #6	$42.89	9.839%	$47.1099	$47.11	$47.10	$47.10
Purchase #7	$164.64	12.617%	$185.4126	$185.41	$185.40	$185.40
7 purchase totals =	$999.34		$1,098.7628	$1,098.76	$1,098.70	$1,098.90