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	$55.88	7.121%	$59.8592	$59.86	$59.85	$59.90
Purchase #2	$36.90	10.472%	$40.7642	$40.76	$40.75	$40.80
Purchase #3	$102.36	7.788%	$110.3318	$110.33	$110.35	$110.30
Purchase #4	$171.54	7.440%	$184.3026	$184.30	$184.30	$184.30
Purchase #5	$36.76	13.644%	$41.7755	$41.78	$41.80	$41.80
Purchase #6	$15.55	10.853%	$17.2376	$17.24	$17.25	$17.20
Purchase #7	$246.52	12.118%	$276.3933	$276.39	$276.40	$276.40
7 purchase totals =	$665.51		$730.6642	$730.66	$730.70	$730.70