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	$93.69	6.352%	$99.6412	$99.64	$99.65	$99.60
Purchase #2	$245.49	12.386%	$275.8964	$275.90	$275.90	$275.90
Purchase #3	$247.37	10.329%	$272.9208	$272.92	$272.90	$272.90
Purchase #4	$100.31	9.235%	$109.5736	$109.57	$109.55	$109.60
Purchase #5	$74.52	3.681%	$77.2631	$77.26	$77.25	$77.30
Purchase #6	$237.45	11.456%	$264.6523	$264.65	$264.65	$264.70
Purchase #7	$201.45	4.206%	$209.923	$209.92	$209.90	$209.90
7 purchase totals =	$1,200.28		$1,309.8704	$1,309.86	$1,309.80	$1,309.90