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	$223.79	11.873%	$250.3606	$250.36	$250.35	$250.40
Purchase #2	$39.83	8.302%	$43.1367	$43.14	$43.15	$43.10
Purchase #3	$125.83	8.436%	$136.445	$136.45	$136.45	$136.40
Purchase #4	$182.38	3.527%	$188.8125	$188.81	$188.80	$188.80
Purchase #5	$174.69	3.349%	$180.5404	$180.54	$180.55	$180.50
Purchase #6	$86.54	4.202%	$90.1764	$90.18	$90.20	$90.20
Purchase #7	$136.54	4.695%	$142.9506	$142.95	$142.95	$143.00
7 purchase totals =	$969.60		$1,032.4222	$1,032.43	$1,032.45	$1,032.40