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	$39.31	7.382%	$42.2119	$42.21	$42.20	$42.20
Purchase #2	$224.72	6.157%	$238.556	$238.56	$238.55	$238.60
Purchase #3	$61.62	7.851%	$66.4578	$66.46	$66.45	$66.50
Purchase #4	$199.32	4.307%	$207.9047	$207.90	$207.90	$207.90
Purchase #5	$59.25	3.264%	$61.1839	$61.18	$61.20	$61.20
Purchase #6	$98.79	7.769%	$106.465	$106.47	$106.45	$106.50
Purchase #7	$209.76	4.749%	$219.7215	$219.72	$219.70	$219.70
7 purchase totals =	$892.77		$942.5008	$942.50	$942.45	$942.60