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	$79.83	3.415%	$82.5562	$82.56	$82.55	$82.60
Purchase #2	$33.89	13.109%	$38.3326	$38.33	$38.35	$38.30
Purchase #3	$228.89	6.290%	$243.2872	$243.29	$243.30	$243.30
Purchase #4	$215.67	8.118%	$233.1781	$233.18	$233.20	$233.20
Purchase #5	$69.32	8.789%	$75.4125	$75.41	$75.40	$75.40
Purchase #6	$27.52	3.595%	$28.5093	$28.51	$28.50	$28.50
Purchase #7	$109.99	12.437%	$123.6695	$123.67	$123.65	$123.70
7 purchase totals =	$765.11		$824.9454	$824.95	$824.95	$825.00