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	$50.95	3.856%	$52.9146	$52.91	$52.90	$52.90
Purchase #2	$79.86	13.558%	$90.6874	$90.69	$90.70	$90.70
Purchase #3	$202.72	6.745%	$216.3935	$216.39	$216.40	$216.40
Purchase #4	$89.83	9.251%	$98.1402	$98.14	$98.15	$98.10
Purchase #5	$145.63	10.789%	$161.342	$161.34	$161.35	$161.30
Purchase #6	$185.91	6.522%	$198.0351	$198.04	$198.05	$198.00
Purchase #7	$247.61	11.156%	$275.2334	$275.23	$275.25	$275.20
7 purchase totals =	$1,002.51		$1,092.7462	$1,092.74	$1,092.80	$1,092.60