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	$82.49	3.481%	$85.3615	$85.36	$85.35	$85.40
Purchase #2	$96.90	12.795%	$109.2984	$109.30	$109.30	$109.30
Purchase #3	$145.82	4.220%	$151.9736	$151.97	$151.95	$152.00
Purchase #4	$94.94	10.469%	$104.8793	$104.88	$104.90	$104.90
Purchase #5	$196.51	11.650%	$219.4034	$219.40	$219.40	$219.40
Purchase #6	$89.41	7.809%	$96.392	$96.39	$96.40	$96.40
Purchase #7	$94.63	9.271%	$103.4031	$103.40	$103.40	$103.40
7 purchase totals =	$800.70		$870.7113	$870.70	$870.70	$870.80