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	$183.33	3.799%	$190.2947	$190.29	$190.30	$190.30
Purchase #2	$18.99	4.538%	$19.8518	$19.85	$19.85	$19.90
Purchase #3	$30.44	11.212%	$33.8529	$33.85	$33.85	$33.90
Purchase #4	$130.89	6.826%	$139.8246	$139.82	$139.80	$139.80
Purchase #5	$88.61	12.458%	$99.649	$99.65	$99.65	$99.60
Purchase #6	$47.62	9.607%	$52.1949	$52.19	$52.20	$52.20
Purchase #7	$222.72	9.178%	$243.1612	$243.16	$243.15	$243.20
7 purchase totals =	$722.60		$778.8291	$778.81	$778.80	$778.90