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	3.810%	$89.9202	$89.92	$89.90	$89.90
Purchase #2	$72.41	12.234%	$81.2686	$81.27	$81.25	$81.30
Purchase #3	$236.91	12.634%	$266.8412	$266.84	$266.85	$266.80
Purchase #4	$69.79	3.695%	$72.3687	$72.37	$72.35	$72.40
Purchase #5	$230.98	13.265%	$261.6195	$261.62	$261.60	$261.60
Purchase #6	$148.61	4.341%	$155.0612	$155.06	$155.05	$155.10
Purchase #7	$221.48	7.272%	$237.586	$237.59	$237.60	$237.60
7 purchase totals =	$1,066.80		$1,164.6654	$1,164.67	$1,164.60	$1,164.70