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	$138.83	6.344%	$147.6374	$147.64	$147.65	$147.60
Purchase #2	$136.32	11.336%	$151.7732	$151.77	$151.75	$151.80
Purchase #3	$216.86	12.192%	$243.2996	$243.30	$243.30	$243.30
Purchase #4	$20.51	5.139%	$21.564	$21.56	$21.55	$21.60
Purchase #5	$72.50	8.805%	$78.8836	$78.88	$78.90	$78.90
Purchase #6	$28.91	10.478%	$31.9392	$31.94	$31.95	$31.90
Purchase #7	$67.86	8.151%	$73.3913	$73.39	$73.40	$73.40
7 purchase totals =	$681.79		$748.4883	$748.48	$748.50	$748.50