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	$51.94	6.603%	$55.3696	$55.37	$55.35	$55.40
Purchase #2	$220.78	13.498%	$250.5809	$250.58	$250.60	$250.60
Purchase #3	$93.25	13.679%	$106.0057	$106.01	$106.00	$106.00
Purchase #4	$182.31	6.370%	$193.9231	$193.92	$193.90	$193.90
Purchase #5	$37.85	13.402%	$42.9227	$42.92	$42.90	$42.90
Purchase #6	$91.71	8.188%	$99.2192	$99.22	$99.20	$99.20
Purchase #7	$75.36	9.340%	$82.3986	$82.40	$82.40	$82.40
7 purchase totals =	$753.20		$830.4198	$830.42	$830.35	$830.40