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	$34.54	7.643%	$37.1799	$37.18	$37.20	$37.20
Purchase #2	$192.54	9.392%	$210.6234	$210.62	$210.60	$210.60
Purchase #3	$89.68	10.423%	$99.0273	$99.03	$99.05	$99.00
Purchase #4	$72.56	10.841%	$80.4262	$80.43	$80.45	$80.40
Purchase #5	$159.26	5.116%	$167.4077	$167.41	$167.40	$167.40
Purchase #6	$86.48	7.334%	$92.8224	$92.82	$92.80	$92.80
Purchase #7	$91.67	5.696%	$96.8915	$96.89	$96.90	$96.90
7 purchase totals =	$726.73		$784.3784	$784.38	$784.40	$784.30