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	$36.61	10.356%	$40.4013	$40.40	$40.40	$40.40
Purchase #2	$91.41	9.547%	$100.1369	$100.14	$100.15	$100.10
Purchase #3	$215.74	12.708%	$243.1562	$243.16	$243.15	$243.20
Purchase #4	$96.37	3.315%	$99.5647	$99.56	$99.55	$99.60
Purchase #5	$196.88	5.525%	$207.7576	$207.76	$207.75	$207.80
Purchase #6	$95.35	4.354%	$99.5015	$99.50	$99.50	$99.50
Purchase #7	$31.48	6.342%	$33.4765	$33.48	$33.50	$33.50
7 purchase totals =	$763.84		$823.9947	$824.00	$824.00	$824.10