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	$111.44	7.786%	$120.1167	$120.12	$120.10	$120.10
Purchase #2	$222.78	10.604%	$246.4036	$246.40	$246.40	$246.40
Purchase #3	$141.51	13.140%	$160.1044	$160.10	$160.10	$160.10
Purchase #4	$198.51	6.532%	$211.4767	$211.48	$211.50	$211.50
Purchase #5	$62.85	6.812%	$67.1313	$67.13	$67.15	$67.10
Purchase #6	$36.59	12.413%	$41.1319	$41.13	$41.15	$41.10
Purchase #7	$49.38	13.317%	$55.9559	$55.96	$55.95	$56.00
7 purchase totals =	$823.06		$902.3205	$902.32	$902.35	$902.30