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	$86.62	3.777%	$89.8916	$89.89	$89.90	$89.90
Purchase #2	$243.57	5.330%	$256.5523	$256.55	$256.55	$256.60
Purchase #3	$109.47	3.754%	$113.5795	$113.58	$113.60	$113.60
Purchase #4	$122.89	5.572%	$129.7374	$129.74	$129.75	$129.70
Purchase #5	$32.36	12.308%	$36.3429	$36.34	$36.35	$36.30
Purchase #6	$176.29	5.464%	$185.9225	$185.92	$185.90	$185.90
Purchase #7	$7.78	12.155%	$8.7257	$8.73	$8.75	$8.70
7 purchase totals =	$778.98		$820.7519	$820.75	$820.80	$820.70