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	$39.41	3.220%	$40.679	$40.68	$40.70	$40.70
Purchase #2	$64.68	3.442%	$66.9063	$66.91	$66.90	$66.90
Purchase #3	$142.74	13.521%	$162.0399	$162.04	$162.05	$162.00
Purchase #4	$23.64	9.547%	$25.8969	$25.90	$25.90	$25.90
Purchase #5	$241.77	13.712%	$274.9215	$274.92	$274.90	$274.90
Purchase #6	$85.70	5.648%	$90.5403	$90.54	$90.55	$90.50
Purchase #7	$243.88	7.167%	$261.3589	$261.36	$261.35	$261.40
7 purchase totals =	$841.82		$922.3428	$922.35	$922.35	$922.30