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	$147.78	5.217%	$155.4897	$155.49	$155.50	$155.50
Purchase #2	$69.94	4.476%	$73.0705	$73.07	$73.05	$73.10
Purchase #3	$140.48	10.578%	$155.34	$155.34	$155.35	$155.30
Purchase #4	$98.62	6.799%	$105.3252	$105.33	$105.35	$105.30
Purchase #5	$39.44	3.763%	$40.9241	$40.92	$40.90	$40.90
Purchase #6	$27.96	12.426%	$31.4343	$31.43	$31.45	$31.40
Purchase #7	$250.61	9.282%	$273.8716	$273.87	$273.85	$273.90
7 purchase totals =	$774.83		$835.4554	$835.45	$835.45	$835.40