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	$21.29	7.453%	$22.8767	$22.88	$22.90	$22.90
Purchase #2	$235.82	5.550%	$248.908	$248.91	$248.90	$248.90
Purchase #3	$35.25	5.186%	$37.0781	$37.08	$37.10	$37.10
Purchase #4	$182.25	4.232%	$189.9628	$189.96	$189.95	$190.00
Purchase #5	$142.56	11.358%	$158.752	$158.75	$158.75	$158.80
Purchase #6	$145.75	4.736%	$152.6527	$152.65	$152.65	$152.70
Purchase #7	$225.91	13.385%	$256.1481	$256.15	$256.15	$256.10
7 purchase totals =	$988.83		$1,066.3784	$1,066.38	$1,066.40	$1,066.50