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	$104.48	13.156%	$118.2254	$118.23	$118.25	$118.20
Purchase #2	$85.89	4.461%	$89.7216	$89.72	$89.70	$89.70
Purchase #3	$79.93	3.251%	$82.5285	$82.53	$82.55	$82.50
Purchase #4	$159.81	6.263%	$169.8189	$169.82	$169.80	$169.80
Purchase #5	$72.37	8.705%	$78.6698	$78.67	$78.65	$78.70
Purchase #6	$129.29	4.552%	$135.1753	$135.18	$135.20	$135.20
Purchase #7	$199.56	9.220%	$217.9594	$217.96	$217.95	$218.00
7 purchase totals =	$831.33		$892.0989	$892.11	$892.10	$892.10