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	$172.25	9.601%	$188.7877	$188.79	$188.80	$188.80
Purchase #2	$138.43	7.544%	$148.8732	$148.87	$148.85	$148.90
Purchase #3	$134.90	12.755%	$152.1065	$152.11	$152.10	$152.10
Purchase #4	$123.25	12.581%	$138.7561	$138.76	$138.75	$138.80
Purchase #5	$241.38	13.649%	$274.326	$274.33	$274.35	$274.30
Purchase #6	$42.25	8.648%	$45.9038	$45.90	$45.90	$45.90
Purchase #7	$229.75	3.619%	$238.0647	$238.06	$238.05	$238.10
7 purchase totals =	$1,082.21		$1,186.8180	$1,186.82	$1,186.80	$1,186.90