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	$202.79	10.414%	$223.9086	$223.91	$223.90	$223.90
Purchase #2	$125.80	8.375%	$136.3358	$136.34	$136.35	$136.30
Purchase #3	$34.86	6.337%	$37.0691	$37.07	$37.05	$37.10
Purchase #4	$82.52	10.672%	$91.3265	$91.33	$91.35	$91.30
Purchase #5	$249.94	11.410%	$278.4582	$278.46	$278.45	$278.50
Purchase #6	$97.87	5.277%	$103.0346	$103.03	$103.05	$103.00
Purchase #7	$243.93	3.871%	$253.3725	$253.37	$253.35	$253.40
7 purchase totals =	$1,037.71		$1,123.5053	$1,123.51	$1,123.50	$1,123.50