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	$83.61	7.207%	$89.6358	$89.64	$89.65	$89.60
Purchase #2	$240.67	3.300%	$248.6121	$248.61	$248.60	$248.60
Purchase #3	$82.84	6.286%	$88.0473	$88.05	$88.05	$88.00
Purchase #4	$56.40	4.640%	$59.017	$59.02	$59.00	$59.00
Purchase #5	$104.48	11.265%	$116.2497	$116.25	$116.25	$116.20
Purchase #6	$213.36	11.871%	$238.688	$238.69	$238.70	$238.70
Purchase #7	$48.63	7.158%	$52.1109	$52.11	$52.10	$52.10
7 purchase totals =	$829.99		$892.3608	$892.37	$892.35	$892.20