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	$242.72	3.473%	$251.1497	$251.15	$251.15	$251.10
Purchase #2	$80.78	7.542%	$86.8724	$86.87	$86.85	$86.90
Purchase #3	$147.96	12.232%	$166.0585	$166.06	$166.05	$166.10
Purchase #4	$48.36	8.750%	$52.5915	$52.59	$52.60	$52.60
Purchase #5	$57.87	11.527%	$64.5407	$64.54	$64.55	$64.50
Purchase #6	$118.57	10.774%	$131.3447	$131.34	$131.35	$131.30
Purchase #7	$34.26	6.872%	$36.6143	$36.61	$36.60	$36.60
7 purchase totals =	$730.52		$789.1718	$789.16	$789.15	$789.10