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	$220.95	13.473%	$250.7186	$250.72	$250.70	$250.70
Purchase #2	$92.96	8.150%	$100.5362	$100.54	$100.55	$100.50
Purchase #3	$111.91	7.365%	$120.1522	$120.15	$120.15	$120.20
Purchase #4	$52.50	13.352%	$59.5098	$59.51	$59.50	$59.50
Purchase #5	$111.73	5.137%	$117.4696	$117.47	$117.45	$117.50
Purchase #6	$196.56	8.550%	$213.3659	$213.37	$213.35	$213.40
Purchase #7	$48.99	13.662%	$55.683	$55.68	$55.70	$55.70
7 purchase totals =	$835.60		$917.4353	$917.44	$917.40	$917.50