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	$62.83	5.242%	$66.1235	$66.12	$66.10	$66.10
Purchase #2	$78.55	8.423%	$85.1663	$85.17	$85.15	$85.20
Purchase #3	$158.88	7.728%	$171.1582	$171.16	$171.15	$171.20
Purchase #4	$168.39	3.259%	$173.8778	$173.88	$173.90	$173.90
Purchase #5	$42.76	10.758%	$47.3601	$47.36	$47.35	$47.40
Purchase #6	$18.83	10.297%	$20.7689	$20.77	$20.75	$20.80
Purchase #7	$206.63	10.454%	$228.2311	$228.23	$228.25	$228.20
7 purchase totals =	$736.87		$792.6859	$792.69	$792.65	$792.80