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	$249.94	3.739%	$259.2853	$259.29	$259.30	$259.30
Purchase #2	$52.85	11.865%	$59.1207	$59.12	$59.10	$59.10
Purchase #3	$84.59	9.528%	$92.6497	$92.65	$92.65	$92.60
Purchase #4	$98.74	10.629%	$109.2351	$109.24	$109.25	$109.20
Purchase #5	$182.59	13.713%	$207.6286	$207.63	$207.65	$207.60
Purchase #6	$59.40	10.380%	$65.5657	$65.57	$65.55	$65.60
Purchase #7	$56.37	11.330%	$62.7567	$62.76	$62.75	$62.80
7 purchase totals =	$784.48		$856.2418	$856.26	$856.25	$856.20