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	$83.54	7.375%	$89.7011	$89.70	$89.70	$89.70
Purchase #2	$110.92	12.186%	$124.4367	$124.44	$124.45	$124.40
Purchase #3	$103.59	4.116%	$107.8538	$107.85	$107.85	$107.90
Purchase #4	$156.43	3.717%	$162.2445	$162.24	$162.25	$162.20
Purchase #5	$82.71	9.728%	$90.756	$90.76	$90.75	$90.80
Purchase #6	$78.80	7.680%	$84.8518	$84.85	$84.85	$84.90
Purchase #7	$91.61	12.303%	$102.8808	$102.88	$102.90	$102.90
7 purchase totals =	$707.60		$762.7247	$762.72	$762.75	$762.80