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	$122.86	4.797%	$128.7536	$128.75	$128.75	$128.80
Purchase #2	$52.64	12.650%	$59.299	$59.30	$59.30	$59.30
Purchase #3	$128.31	11.387%	$142.9207	$142.92	$142.90	$142.90
Purchase #4	$130.34	10.285%	$143.7455	$143.75	$143.75	$143.70
Purchase #5	$227.43	10.777%	$251.9401	$251.94	$251.95	$251.90
Purchase #6	$243.49	12.280%	$273.3906	$273.39	$273.40	$273.40
Purchase #7	$133.90	9.160%	$146.1652	$146.17	$146.15	$146.20
7 purchase totals =	$1,038.97		$1,146.2147	$1,146.22	$1,146.20	$1,146.20