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	$35.85	5.486%	$37.8167	$37.82	$37.80	$37.80
Purchase #2	$133.96	4.764%	$140.3419	$140.34	$140.35	$140.30
Purchase #3	$162.87	5.282%	$171.4728	$171.47	$171.45	$171.50
Purchase #4	$164.53	9.242%	$179.7359	$179.74	$179.75	$179.70
Purchase #5	$116.28	4.805%	$121.8673	$121.87	$121.85	$121.90
Purchase #6	$176.45	8.344%	$191.173	$191.17	$191.15	$191.20
Purchase #7	$29.96	8.599%	$32.5363	$32.54	$32.55	$32.50
7 purchase totals =	$819.90		$874.9439	$874.95	$874.90	$874.90