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	$240.83	8.598%	$261.5366	$261.54	$261.55	$261.50
Purchase #2	$101.89	10.820%	$112.9145	$112.91	$112.90	$112.90
Purchase #3	$87.50	10.246%	$96.4653	$96.47	$96.45	$96.50
Purchase #4	$128.33	3.562%	$132.9011	$132.90	$132.90	$132.90
Purchase #5	$148.63	11.220%	$165.3063	$165.31	$165.30	$165.30
Purchase #6	$73.86	12.303%	$82.947	$82.95	$82.95	$82.90
Purchase #7	$97.28	7.688%	$104.7589	$104.76	$104.75	$104.80
7 purchase totals =	$878.32		$956.8297	$956.84	$956.80	$956.80