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	$139.92	7.813%	$150.8519	$150.85	$150.85	$150.90
Purchase #2	$109.43	4.108%	$113.9254	$113.93	$113.95	$113.90
Purchase #3	$38.53	9.441%	$42.1676	$42.17	$42.15	$42.20
Purchase #4	$225.89	11.413%	$251.6708	$251.67	$251.65	$251.70
Purchase #5	$87.44	13.751%	$99.4639	$99.46	$99.45	$99.50
Purchase #6	$223.79	5.754%	$236.6669	$236.67	$236.65	$236.70
Purchase #7	$43.65	3.336%	$45.1062	$45.11	$45.10	$45.10
7 purchase totals =	$868.65		$939.8527	$939.86	$939.80	$940.00