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	$89.95	11.545%	$100.3347	$100.33	$100.35	$100.30
Purchase #2	$18.70	8.364%	$20.2641	$20.26	$20.25	$20.30
Purchase #3	$80.32	3.519%	$83.1465	$83.15	$83.15	$83.10
Purchase #4	$209.89	6.466%	$223.4615	$223.46	$223.45	$223.50
Purchase #5	$64.90	12.637%	$73.1014	$73.10	$73.10	$73.10
Purchase #6	$54.73	11.401%	$60.9698	$60.97	$60.95	$61.00
Purchase #7	$184.51	13.445%	$209.3174	$209.32	$209.30	$209.30
7 purchase totals =	$703.00		$770.5954	$770.59	$770.55	$770.60