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	$165.29	12.123%	$185.3281	$185.33	$185.35	$185.30
Purchase #2	$63.26	11.603%	$70.6001	$70.60	$70.60	$70.60
Purchase #3	$65.51	12.226%	$73.5193	$73.52	$73.50	$73.50
Purchase #4	$71.76	3.507%	$74.2766	$74.28	$74.30	$74.30
Purchase #5	$121.69	12.480%	$136.8769	$136.88	$136.90	$136.90
Purchase #6	$214.74	3.828%	$222.9602	$222.96	$222.95	$223.00
Purchase #7	$128.53	9.516%	$140.7609	$140.76	$140.75	$140.80
7 purchase totals =	$830.78		$904.3221	$904.33	$904.35	$904.40