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	$199.74	3.222%	$206.1756	$206.18	$206.20	$206.20
Purchase #2	$59.49	3.354%	$61.4853	$61.49	$61.50	$61.50
Purchase #3	$87.37	13.277%	$98.9701	$98.97	$98.95	$99.00
Purchase #4	$188.33	4.556%	$196.9103	$196.91	$196.90	$196.90
Purchase #5	$248.47	11.290%	$276.5223	$276.52	$276.50	$276.50
Purchase #6	$90.98	10.104%	$100.1726	$100.17	$100.15	$100.20
Purchase #7	$65.41	12.350%	$73.4881	$73.49	$73.50	$73.50
7 purchase totals =	$939.79		$1,013.7243	$1,013.73	$1,013.70	$1,013.80