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	$27.35	6.550%	$29.1414	$29.14	$29.15	$29.10
Purchase #2	$238.74	6.753%	$254.8621	$254.86	$254.85	$254.90
Purchase #3	$203.57	3.793%	$211.2914	$211.29	$211.30	$211.30
Purchase #4	$128.36	8.301%	$139.0152	$139.02	$139.00	$139.00
Purchase #5	$42.79	8.457%	$46.4088	$46.41	$46.40	$46.40
Purchase #6	$128.36	4.359%	$133.9552	$133.96	$133.95	$134.00
Purchase #7	$173.38	13.575%	$196.9163	$196.92	$196.90	$196.90
7 purchase totals =	$942.55		$1,011.5904	$1,011.60	$1,011.55	$1,011.60