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	$96.88	3.508%	$100.2786	$100.28	$100.30	$100.30
Purchase #2	$32.87	13.851%	$37.4228	$37.42	$37.40	$37.40
Purchase #3	$112.56	11.209%	$125.1769	$125.18	$125.20	$125.20
Purchase #4	$147.89	12.173%	$165.8926	$165.89	$165.90	$165.90
Purchase #5	$117.69	4.438%	$122.9131	$122.91	$122.90	$122.90
Purchase #6	$199.68	5.614%	$210.89	$210.89	$210.90	$210.90
Purchase #7	$113.91	10.319%	$125.6644	$125.66	$125.65	$125.70
7 purchase totals =	$821.48		$888.2384	$888.23	$888.25	$888.30