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	$104.59	4.447%	$109.2411	$109.24	$109.25	$109.20
Purchase #2	$210.45	8.840%	$229.0538	$229.05	$229.05	$229.10
Purchase #3	$90.62	10.253%	$99.9113	$99.91	$99.90	$99.90
Purchase #4	$185.38	8.697%	$201.5025	$201.50	$201.50	$201.50
Purchase #5	$108.82	11.268%	$121.0818	$121.08	$121.10	$121.10
Purchase #6	$18.59	13.760%	$21.148	$21.15	$21.15	$21.10
Purchase #7	$60.52	10.869%	$67.0979	$67.10	$67.10	$67.10
7 purchase totals =	$778.97		$849.0364	$849.03	$849.05	$849.00