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	$134.60	3.786%	$139.696	$139.70	$139.70	$139.70
Purchase #2	$195.56	13.788%	$222.5238	$222.52	$222.50	$222.50
Purchase #3	$86.99	3.357%	$89.9103	$89.91	$89.90	$89.90
Purchase #4	$120.74	8.647%	$131.1804	$131.18	$131.20	$131.20
Purchase #5	$67.98	5.484%	$71.708	$71.71	$71.70	$71.70
Purchase #6	$211.59	6.711%	$225.7898	$225.79	$225.80	$225.80
Purchase #7	$98.59	6.707%	$105.2024	$105.20	$105.20	$105.20
7 purchase totals =	$916.05		$986.0107	$986.01	$986.00	$986.00