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	$120.72	10.287%	$133.1385	$133.14	$133.15	$133.10
Purchase #2	$36.25	11.728%	$40.5014	$40.50	$40.50	$40.50
Purchase #3	$133.97	12.212%	$150.3304	$150.33	$150.35	$150.30
Purchase #4	$215.34	12.803%	$242.91	$242.91	$242.90	$242.90
Purchase #5	$32.28	9.489%	$35.343	$35.34	$35.35	$35.30
Purchase #6	$88.44	12.230%	$99.2562	$99.26	$99.25	$99.30
Purchase #7	$36.42	12.843%	$41.0974	$41.10	$41.10	$41.10
7 purchase totals =	$663.42		$742.5769	$742.58	$742.60	$742.50