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	$39.70	13.629%	$45.1107	$45.11	$45.10	$45.10
Purchase #2	$73.57	6.737%	$78.5264	$78.53	$78.55	$78.50
Purchase #3	$97.58	9.504%	$106.854	$106.85	$106.85	$106.90
Purchase #4	$120.98	8.828%	$131.6601	$131.66	$131.65	$131.70
Purchase #5	$249.63	13.503%	$283.3375	$283.34	$283.35	$283.30
Purchase #6	$74.39	5.299%	$78.3319	$78.33	$78.35	$78.30
Purchase #7	$238.52	4.297%	$248.7692	$248.77	$248.75	$248.80
7 purchase totals =	$894.37		$972.5898	$972.59	$972.60	$972.60