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	$190.48	10.498%	$210.4766	$210.48	$210.50	$210.50
Purchase #2	$35.42	4.766%	$37.1081	$37.11	$37.10	$37.10
Purchase #3	$124.37	12.204%	$139.5481	$139.55	$139.55	$139.50
Purchase #4	$36.52	10.429%	$40.3287	$40.33	$40.35	$40.30
Purchase #5	$85.45	12.555%	$96.1782	$96.18	$96.20	$96.20
Purchase #6	$206.25	13.171%	$233.4152	$233.42	$233.40	$233.40
Purchase #7	$161.66	8.471%	$175.3542	$175.35	$175.35	$175.40
7 purchase totals =	$840.15		$932.4091	$932.42	$932.45	$932.40