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	$200.71	10.685%	$222.1559	$222.16	$222.15	$222.20
Purchase #2	$109.71	3.145%	$113.1604	$113.16	$113.15	$113.20
Purchase #3	$172.71	13.496%	$196.0189	$196.02	$196.00	$196.00
Purchase #4	$165.63	3.808%	$171.9372	$171.94	$171.95	$171.90
Purchase #5	$129.55	11.850%	$144.9017	$144.90	$144.90	$144.90
Purchase #6	$7.34	12.701%	$8.2723	$8.27	$8.25	$8.30
Purchase #7	$61.95	12.858%	$69.9155	$69.92	$69.90	$69.90
7 purchase totals =	$847.60		$926.3619	$926.37	$926.30	$926.40