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	$170.35	8.761%	$185.2744	$185.27	$185.25	$185.30
Purchase #2	$117.69	11.539%	$131.2702	$131.27	$131.25	$131.30
Purchase #3	$79.56	5.229%	$83.7202	$83.72	$83.70	$83.70
Purchase #4	$214.40	11.132%	$238.267	$238.27	$238.25	$238.30
Purchase #5	$21.63	7.317%	$23.2127	$23.21	$23.20	$23.20
Purchase #6	$247.35	7.169%	$265.0825	$265.08	$265.10	$265.10
Purchase #7	$243.50	12.543%	$274.0422	$274.04	$274.05	$274.00
7 purchase totals =	$1,094.48		$1,200.8692	$1,200.86	$1,200.80	$1,200.90