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	$30.25	12.751%	$34.1072	$34.11	$34.10	$34.10
Purchase #2	$111.33	4.666%	$116.5247	$116.52	$116.50	$116.50
Purchase #3	$174.95	9.651%	$191.8344	$191.83	$191.85	$191.80
Purchase #4	$213.47	4.713%	$223.5308	$223.53	$223.55	$223.50
Purchase #5	$22.72	10.145%	$25.0249	$25.02	$25.00	$25.00
Purchase #6	$182.71	7.273%	$195.9985	$196.00	$196.00	$196.00
Purchase #7	$181.40	6.365%	$192.9461	$192.95	$192.95	$192.90
7 purchase totals =	$916.83		$979.9666	$979.96	$979.95	$979.80