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	$31.50	9.690%	$34.5524	$34.55	$34.55	$34.60
Purchase #2	$232.79	5.375%	$245.3025	$245.30	$245.30	$245.30
Purchase #3	$181.47	4.288%	$189.2514	$189.25	$189.25	$189.30
Purchase #4	$181.59	3.731%	$188.3651	$188.37	$188.35	$188.40
Purchase #5	$176.50	12.448%	$198.4707	$198.47	$198.45	$198.50
Purchase #6	$136.52	7.313%	$146.5037	$146.50	$146.50	$146.50
Purchase #7	$198.48	10.722%	$219.761	$219.76	$219.75	$219.80
7 purchase totals =	$1,138.85		$1,222.2068	$1,222.20	$1,222.15	$1,222.40