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	$119.92	7.477%	$128.8864	$128.89	$128.90	$128.90
Purchase #2	$95.73	3.535%	$99.1141	$99.11	$99.10	$99.10
Purchase #3	$229.29	13.172%	$259.4921	$259.49	$259.50	$259.50
Purchase #4	$211.43	6.479%	$225.1285	$225.13	$225.15	$225.10
Purchase #5	$216.66	11.858%	$242.3515	$242.35	$242.35	$242.40
Purchase #6	$239.36	13.135%	$270.7999	$270.80	$270.80	$270.80
Purchase #7	$172.74	3.615%	$178.9846	$178.98	$179.00	$179.00
7 purchase totals =	$1,285.13		$1,404.7571	$1,404.75	$1,404.80	$1,404.80