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	$166.98	3.336%	$172.5505	$172.55	$172.55	$172.60
Purchase #2	$83.60	6.537%	$89.0649	$89.06	$89.05	$89.10
Purchase #3	$162.28	12.281%	$182.2096	$182.21	$182.20	$182.20
Purchase #4	$160.74	9.408%	$175.8624	$175.86	$175.85	$175.90
Purchase #5	$95.44	8.594%	$103.6421	$103.64	$103.65	$103.60
Purchase #6	$77.90	7.676%	$83.8796	$83.88	$83.90	$83.90
Purchase #7	$37.85	13.166%	$42.8333	$42.83	$42.85	$42.80
7 purchase totals =	$784.79		$850.0424	$850.03	$850.05	$850.10