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	$165.89	3.368%	$171.4772	$171.48	$171.50	$171.50
Purchase #2	$245.39	3.547%	$254.094	$254.09	$254.10	$254.10
Purchase #3	$223.82	6.588%	$238.5653	$238.57	$238.55	$238.60
Purchase #4	$106.25	9.656%	$116.5095	$116.51	$116.50	$116.50
Purchase #5	$37.56	4.499%	$39.2498	$39.25	$39.25	$39.20
Purchase #6	$98.71	5.121%	$103.7649	$103.76	$103.75	$103.80
Purchase #7	$233.59	12.378%	$262.5038	$262.50	$262.50	$262.50
7 purchase totals =	$1,111.21		$1,186.1645	$1,186.16	$1,186.15	$1,186.20