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	$149.42	3.821%	$155.1293	$155.13	$155.15	$155.10
Purchase #2	$94.81	5.192%	$99.7325	$99.73	$99.75	$99.70
Purchase #3	$168.29	11.703%	$187.985	$187.99	$188.00	$188.00
Purchase #4	$37.57	13.129%	$42.5026	$42.50	$42.50	$42.50
Purchase #5	$221.53	3.456%	$229.1861	$229.19	$229.20	$229.20
Purchase #6	$241.35	13.347%	$273.563	$273.56	$273.55	$273.60
Purchase #7	$96.72	6.723%	$103.2225	$103.22	$103.20	$103.20
7 purchase totals =	$1,009.69		$1,091.3210	$1,091.32	$1,091.35	$1,091.30