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	$231.36	8.117%	$250.1395	$250.14	$250.15	$250.10
Purchase #2	$89.90	10.513%	$99.3512	$99.35	$99.35	$99.40
Purchase #3	$5.70	9.135%	$6.2207	$6.22	$6.20	$6.20
Purchase #4	$162.27	8.538%	$176.1246	$176.12	$176.10	$176.10
Purchase #5	$182.50	7.593%	$196.3572	$196.36	$196.35	$196.40
Purchase #6	$183.66	11.279%	$204.375	$204.38	$204.40	$204.40
Purchase #7	$148.89	6.555%	$158.6497	$158.65	$158.65	$158.60
7 purchase totals =	$1,004.28		$1,091.2179	$1,091.22	$1,091.20	$1,091.20