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	$223.73	9.873%	$245.8189	$245.82	$245.80	$245.80
Purchase #2	$223.78	12.163%	$250.9984	$251.00	$251.00	$251.00
Purchase #3	$29.91	8.602%	$32.4829	$32.48	$32.50	$32.50
Purchase #4	$191.70	7.650%	$206.3651	$206.37	$206.35	$206.40
Purchase #5	$148.56	11.355%	$165.429	$165.43	$165.45	$165.40
Purchase #6	$136.58	7.749%	$147.1636	$147.16	$147.15	$147.20
Purchase #7	$39.52	9.834%	$43.4064	$43.41	$43.40	$43.40
7 purchase totals =	$993.78		$1,091.6643	$1,091.67	$1,091.65	$1,091.70