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	$60.76	12.556%	$68.389	$68.39	$68.40	$68.40
Purchase #2	$134.33	4.854%	$140.8504	$140.85	$140.85	$140.90
Purchase #3	$246.73	6.687%	$263.2288	$263.23	$263.25	$263.20
Purchase #4	$205.68	8.612%	$223.3932	$223.39	$223.40	$223.40
Purchase #5	$43.98	4.701%	$46.0475	$46.05	$46.05	$46.00
Purchase #6	$155.43	4.499%	$162.4228	$162.42	$162.40	$162.40
Purchase #7	$87.36	13.868%	$99.4751	$99.48	$99.50	$99.50
7 purchase totals =	$934.27		$1,003.8068	$1,003.81	$1,003.85	$1,003.80