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	$108.61	3.392%	$112.2941	$112.29	$112.30	$112.30
Purchase #2	$50.42	6.281%	$53.5869	$53.59	$53.60	$53.60
Purchase #3	$83.70	12.754%	$94.3751	$94.38	$94.40	$94.40
Purchase #4	$204.34	3.860%	$212.2275	$212.23	$212.25	$212.20
Purchase #5	$78.39	9.624%	$85.9343	$85.93	$85.95	$85.90
Purchase #6	$89.78	10.202%	$98.9394	$98.94	$98.95	$98.90
Purchase #7	$136.31	11.805%	$152.4014	$152.40	$152.40	$152.40
7 purchase totals =	$751.55		$809.7587	$809.76	$809.85	$809.70