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	$129.40	8.864%	$140.87	$140.87	$140.85	$140.90
Purchase #2	$141.57	4.423%	$147.8316	$147.83	$147.85	$147.80
Purchase #3	$40.98	6.230%	$43.5331	$43.53	$43.55	$43.50
Purchase #4	$108.37	10.621%	$119.88	$119.88	$119.90	$119.90
Purchase #5	$122.29	9.612%	$134.0445	$134.04	$134.05	$134.00
Purchase #6	$96.63	8.816%	$105.1489	$105.15	$105.15	$105.10
Purchase #7	$155.29	6.459%	$165.3202	$165.32	$165.30	$165.30
7 purchase totals =	$794.53		$856.6283	$856.62	$856.65	$856.50