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	$38.75	11.354%	$43.1497	$43.15	$43.15	$43.10
Purchase #2	$16.81	9.428%	$18.3948	$18.39	$18.40	$18.40
Purchase #3	$143.72	6.400%	$152.9181	$152.92	$152.90	$152.90
Purchase #4	$188.38	11.610%	$210.2509	$210.25	$210.25	$210.30
Purchase #5	$233.33	13.796%	$265.5202	$265.52	$265.50	$265.50
Purchase #6	$64.94	12.362%	$72.9679	$72.97	$72.95	$73.00
Purchase #7	$104.96	5.317%	$110.5407	$110.54	$110.55	$110.50
7 purchase totals =	$790.89		$873.7423	$873.74	$873.70	$873.70