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	$93.66	6.150%	$99.4201	$99.42	$99.40	$99.40
Purchase #2	$64.60	4.581%	$67.5593	$67.56	$67.55	$67.60
Purchase #3	$24.68	10.619%	$27.3008	$27.30	$27.30	$27.30
Purchase #4	$27.90	3.691%	$28.9298	$28.93	$28.95	$28.90
Purchase #5	$20.59	8.479%	$22.3358	$22.34	$22.35	$22.30
Purchase #6	$47.36	12.590%	$53.3226	$53.32	$53.30	$53.30
Purchase #7	$119.29	12.475%	$134.1714	$134.17	$134.15	$134.20
7 purchase totals =	$398.08		$433.0398	$433.04	$433.00	$433.00