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	$19.27	6.263%	$20.4769	$20.48	$20.50	$20.50
Purchase #2	$79.43	12.611%	$89.4469	$89.45	$89.45	$89.40
Purchase #3	$213.50	4.301%	$222.6826	$222.68	$222.70	$222.70
Purchase #4	$200.37	3.374%	$207.1305	$207.13	$207.15	$207.10
Purchase #5	$94.94	3.715%	$98.467	$98.47	$98.45	$98.50
Purchase #6	$105.39	3.804%	$109.399	$109.40	$109.40	$109.40
Purchase #7	$86.87	5.609%	$91.7425	$91.74	$91.75	$91.70
7 purchase totals =	$799.77		$839.3454	$839.35	$839.40	$839.30