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	$55.41	6.870%	$59.2167	$59.22	$59.20	$59.20
Purchase #2	$227.46	11.687%	$254.0433	$254.04	$254.05	$254.00
Purchase #3	$89.54	9.281%	$97.8502	$97.85	$97.85	$97.90
Purchase #4	$45.49	13.863%	$51.7963	$51.80	$51.80	$51.80
Purchase #5	$83.73	4.234%	$87.2751	$87.28	$87.30	$87.30
Purchase #6	$170.68	5.774%	$180.5351	$180.54	$180.55	$180.50
Purchase #7	$32.54	11.337%	$36.2291	$36.23	$36.25	$36.20
7 purchase totals =	$704.85		$766.9458	$766.96	$767.00	$766.90