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	$202.77	10.383%	$223.8236	$223.82	$223.80	$223.80
Purchase #2	$236.63	3.362%	$244.5855	$244.59	$244.60	$244.60
Purchase #3	$216.71	3.833%	$225.0165	$225.02	$225.00	$225.00
Purchase #4	$35.71	5.168%	$37.5555	$37.56	$37.55	$37.60
Purchase #5	$84.89	5.269%	$89.3629	$89.36	$89.35	$89.40
Purchase #6	$210.62	3.423%	$217.8295	$217.83	$217.85	$217.80
Purchase #7	$117.98	11.792%	$131.8922	$131.89	$131.90	$131.90
7 purchase totals =	$1,105.31		$1,170.0657	$1,170.07	$1,170.05	$1,170.10