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	$134.56	12.849%	$151.8496	$151.85	$151.85	$151.80
Purchase #2	$217.32	10.578%	$240.3081	$240.31	$240.30	$240.30
Purchase #3	$74.78	11.286%	$83.2197	$83.22	$83.20	$83.20
Purchase #4	$138.36	6.407%	$147.2247	$147.22	$147.20	$147.20
Purchase #5	$243.68	9.421%	$266.6371	$266.64	$266.65	$266.60
Purchase #6	$117.37	6.380%	$124.8582	$124.86	$124.85	$124.90
Purchase #7	$90.38	4.128%	$94.1109	$94.11	$94.10	$94.10
7 purchase totals =	$1,016.45		$1,108.2083	$1,108.21	$1,108.15	$1,108.10