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	$165.43	3.680%	$171.5178	$171.52	$171.50	$171.50
Purchase #2	$18.44	9.243%	$20.1444	$20.14	$20.15	$20.10
Purchase #3	$216.66	13.550%	$246.0174	$246.02	$246.00	$246.00
Purchase #4	$174.99	11.841%	$195.7106	$195.71	$195.70	$195.70
Purchase #5	$73.33	12.446%	$82.4567	$82.46	$82.45	$82.50
Purchase #6	$112.26	3.336%	$116.005	$116.01	$116.00	$116.00
Purchase #7	$156.54	9.606%	$171.5772	$171.58	$171.60	$171.60
7 purchase totals =	$917.65		$1,003.4291	$1,003.44	$1,003.40	$1,003.40