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	$24.36	11.147%	$27.0754	$27.08	$27.10	$27.10
Purchase #2	$216.82	12.158%	$243.181	$243.18	$243.20	$243.20
Purchase #3	$72.58	13.725%	$82.5416	$82.54	$82.55	$82.50
Purchase #4	$115.81	8.427%	$125.5693	$125.57	$125.55	$125.60
Purchase #5	$208.64	11.732%	$233.1176	$233.12	$233.10	$233.10
Purchase #6	$97.89	11.686%	$109.3294	$109.33	$109.35	$109.30
Purchase #7	$250.33	10.632%	$276.9451	$276.95	$276.95	$276.90
7 purchase totals =	$986.43		$1,097.7594	$1,097.77	$1,097.80	$1,097.70