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	$227.35	6.846%	$242.9144	$242.91	$242.90	$242.90
Purchase #2	$194.61	13.672%	$221.2171	$221.22	$221.20	$221.20
Purchase #3	$187.74	4.406%	$196.0118	$196.01	$196.00	$196.00
Purchase #4	$85.49	5.310%	$90.0295	$90.03	$90.05	$90.00
Purchase #5	$120.84	7.589%	$130.0105	$130.01	$130.00	$130.00
Purchase #6	$124.34	3.390%	$128.5551	$128.56	$128.55	$128.60
Purchase #7	$208.61	5.430%	$219.9375	$219.94	$219.95	$219.90
7 purchase totals =	$1,148.98		$1,228.6759	$1,228.68	$1,228.65	$1,228.60