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	$39.85	7.714%	$42.924	$42.92	$42.90	$42.90
Purchase #2	$19.33	13.715%	$21.9811	$21.98	$22.00	$22.00
Purchase #3	$105.36	5.602%	$111.2623	$111.26	$111.25	$111.30
Purchase #4	$142.79	3.122%	$147.2479	$147.25	$147.25	$147.20
Purchase #5	$37.89	13.166%	$42.8786	$42.88	$42.90	$42.90
Purchase #6	$113.66	9.557%	$124.5225	$124.52	$124.50	$124.50
Purchase #7	$99.65	5.864%	$105.4935	$105.49	$105.50	$105.50
7 purchase totals =	$558.53		$596.3099	$596.30	$596.30	$596.30