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	$69.39	5.648%	$73.3091	$73.31	$73.30	$73.30
Purchase #2	$67.39	6.123%	$71.5163	$71.52	$71.50	$71.50
Purchase #3	$80.57	6.745%	$86.0044	$86.00	$86.00	$86.00
Purchase #4	$49.39	7.588%	$53.1377	$53.14	$53.15	$53.10
Purchase #5	$146.76	12.354%	$164.8907	$164.89	$164.90	$164.90
Purchase #6	$165.53	12.777%	$186.6798	$186.68	$186.70	$186.70
Purchase #7	$32.76	4.216%	$34.1412	$34.14	$34.15	$34.10
7 purchase totals =	$611.79		$669.6792	$669.68	$669.70	$669.60