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	$209.31	3.501%	$216.6379	$216.64	$216.65	$216.60
Purchase #2	$32.70	8.681%	$35.5387	$35.54	$35.55	$35.50
Purchase #3	$182.35	9.205%	$199.1353	$199.14	$199.15	$199.10
Purchase #4	$162.71	5.357%	$171.4264	$171.43	$171.45	$171.40
Purchase #5	$143.58	13.104%	$162.3947	$162.39	$162.40	$162.40
Purchase #6	$94.46	5.867%	$100.002	$100.00	$100.00	$100.00
Purchase #7	$81.56	9.432%	$89.2527	$89.25	$89.25	$89.30
7 purchase totals =	$906.67		$974.3877	$974.39	$974.45	$974.30