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	$37.89	3.474%	$39.2063	$39.21	$39.20	$39.20
Purchase #2	$35.44	5.726%	$37.4693	$37.47	$37.45	$37.50
Purchase #3	$243.38	11.459%	$271.2689	$271.27	$271.25	$271.30
Purchase #4	$246.66	12.830%	$278.3065	$278.31	$278.30	$278.30
Purchase #5	$155.92	10.650%	$172.5255	$172.53	$172.55	$172.50
Purchase #6	$30.32	6.120%	$32.1756	$32.18	$32.20	$32.20
Purchase #7	$188.70	6.663%	$201.2731	$201.27	$201.25	$201.30
7 purchase totals =	$938.31		$1,032.2252	$1,032.24	$1,032.20	$1,032.30