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	$130.27	9.167%	$142.2119	$142.21	$142.20	$142.20
Purchase #2	$74.82	12.206%	$83.9525	$83.95	$83.95	$84.00
Purchase #3	$38.73	6.227%	$41.1417	$41.14	$41.15	$41.10
Purchase #4	$228.27	12.213%	$256.1486	$256.15	$256.15	$256.10
Purchase #5	$109.38	13.180%	$123.7963	$123.80	$123.80	$123.80
Purchase #6	$82.36	8.362%	$89.2469	$89.25	$89.25	$89.20
Purchase #7	$125.57	7.496%	$134.9827	$134.98	$135.00	$135.00
7 purchase totals =	$789.40		$871.4806	$871.48	$871.50	$871.40