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	$129.30	6.345%	$137.5041	$137.50	$137.50	$137.50
Purchase #2	$130.49	3.180%	$134.6396	$134.64	$134.65	$134.60
Purchase #3	$91.34	9.602%	$100.1105	$100.11	$100.10	$100.10
Purchase #4	$160.30	7.180%	$171.8095	$171.81	$171.80	$171.80
Purchase #5	$187.86	13.790%	$213.7659	$213.77	$213.75	$213.80
Purchase #6	$187.28	9.122%	$204.3637	$204.36	$204.35	$204.40
Purchase #7	$139.35	7.846%	$150.2834	$150.28	$150.30	$150.30
7 purchase totals =	$1,025.92		$1,112.4767	$1,112.47	$1,112.45	$1,112.50