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	$175.70	7.153%	$188.2678	$188.27	$188.25	$188.30
Purchase #2	$18.66	11.798%	$20.8615	$20.86	$20.85	$20.90
Purchase #3	$99.54	3.551%	$103.0747	$103.07	$103.05	$103.10
Purchase #4	$29.58	6.365%	$31.4628	$31.46	$31.45	$31.50
Purchase #5	$249.96	4.731%	$261.7856	$261.79	$261.80	$261.80
Purchase #6	$24.32	6.402%	$25.877	$25.88	$25.90	$25.90
Purchase #7	$157.36	7.210%	$168.7057	$168.71	$168.70	$168.70
7 purchase totals =	$755.12		$800.0351	$800.04	$800.00	$800.20