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	$33.87	11.850%	$37.8836	$37.88	$37.90	$37.90
Purchase #2	$96.37	9.236%	$105.2707	$105.27	$105.25	$105.30
Purchase #3	$210.98	6.418%	$224.5207	$224.52	$224.50	$224.50
Purchase #4	$211.65	4.429%	$221.024	$221.02	$221.00	$221.00
Purchase #5	$232.80	9.820%	$255.661	$255.66	$255.65	$255.70
Purchase #6	$135.46	10.835%	$150.1371	$150.14	$150.15	$150.10
Purchase #7	$236.79	4.540%	$247.5403	$247.54	$247.55	$247.50
7 purchase totals =	$1,157.92		$1,242.0374	$1,242.03	$1,242.00	$1,242.00