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	$59.83	12.391%	$67.2435	$67.24	$67.25	$67.20
Purchase #2	$114.36	11.344%	$127.333	$127.33	$127.35	$127.30
Purchase #3	$6.30	11.220%	$7.0069	$7.01	$7.00	$7.00
Purchase #4	$69.84	3.700%	$72.4241	$72.42	$72.40	$72.40
Purchase #5	$230.34	11.207%	$256.1542	$256.15	$256.15	$256.20
Purchase #6	$106.29	10.387%	$117.3303	$117.33	$117.35	$117.30
Purchase #7	$246.82	9.682%	$270.7171	$270.72	$270.70	$270.70
7 purchase totals =	$833.78		$918.2091	$918.20	$918.20	$918.10