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	$6.86	4.445%	$7.1649	$7.16	$7.15	$7.20
Purchase #2	$207.93	7.664%	$223.8658	$223.87	$223.85	$223.90
Purchase #3	$123.29	6.380%	$131.1559	$131.16	$131.15	$131.20
Purchase #4	$104.57	4.320%	$109.0874	$109.09	$109.10	$109.10
Purchase #5	$86.43	9.744%	$94.8517	$94.85	$94.85	$94.90
Purchase #6	$194.75	13.814%	$221.6528	$221.65	$221.65	$221.70
Purchase #7	$58.93	13.134%	$66.6699	$66.67	$66.65	$66.70
7 purchase totals =	$782.76		$854.4484	$854.45	$854.40	$854.70