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	$130.32	3.193%	$134.4811	$134.48	$134.50	$134.50
Purchase #2	$129.40	8.610%	$140.5413	$140.54	$140.55	$140.50
Purchase #3	$220.45	10.350%	$243.2666	$243.27	$243.25	$243.30
Purchase #4	$62.68	13.730%	$71.286	$71.29	$71.30	$71.30
Purchase #5	$142.60	3.201%	$147.1646	$147.16	$147.15	$147.20
Purchase #6	$172.35	6.146%	$182.9426	$182.94	$182.95	$182.90
Purchase #7	$196.38	6.371%	$208.8914	$208.89	$208.90	$208.90
7 purchase totals =	$1,054.18		$1,128.5736	$1,128.57	$1,128.60	$1,128.60