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	$244.30	12.403%	$274.6005	$274.60	$274.60	$274.60
Purchase #2	$51.81	3.730%	$53.7425	$53.74	$53.75	$53.70
Purchase #3	$233.76	8.806%	$254.3449	$254.34	$254.35	$254.30
Purchase #4	$117.36	12.397%	$131.9091	$131.91	$131.90	$131.90
Purchase #5	$236.47	3.855%	$245.5859	$245.59	$245.60	$245.60
Purchase #6	$214.44	13.579%	$243.5588	$243.56	$243.55	$243.60
Purchase #7	$47.55	10.623%	$52.6012	$52.60	$52.60	$52.60
7 purchase totals =	$1,145.69		$1,256.3429	$1,256.34	$1,256.35	$1,256.30