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	$161.76	5.832%	$171.1938	$171.19	$171.20	$171.20
Purchase #2	$98.27	7.802%	$105.937	$105.94	$105.95	$105.90
Purchase #3	$156.29	10.360%	$172.4816	$172.48	$172.50	$172.50
Purchase #4	$193.94	5.197%	$204.0191	$204.02	$204.00	$204.00
Purchase #5	$155.61	12.279%	$174.7174	$174.72	$174.70	$174.70
Purchase #6	$25.46	8.606%	$27.6511	$27.65	$27.65	$27.70
Purchase #7	$111.41	5.448%	$117.4796	$117.48	$117.50	$117.50
7 purchase totals =	$902.74		$973.4796	$973.48	$973.50	$973.50