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	$45.79	9.333%	$50.0636	$50.06	$50.05	$50.10
Purchase #2	$67.69	4.482%	$70.7239	$70.72	$70.70	$70.70
Purchase #3	$223.56	5.544%	$235.9542	$235.95	$235.95	$236.00
Purchase #4	$124.36	12.807%	$140.2868	$140.29	$140.30	$140.30
Purchase #5	$74.73	7.667%	$80.4595	$80.46	$80.45	$80.50
Purchase #6	$39.26	8.176%	$42.4699	$42.47	$42.45	$42.50
Purchase #7	$152.44	10.645%	$168.6672	$168.67	$168.65	$168.70
7 purchase totals =	$727.83		$788.6251	$788.62	$788.55	$788.80