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	$6.90	9.197%	$7.5346	$7.53	$7.55	$7.50
Purchase #2	$72.89	8.234%	$78.8918	$78.89	$78.90	$78.90
Purchase #3	$149.96	9.476%	$164.1702	$164.17	$164.15	$164.20
Purchase #4	$79.47	9.243%	$86.8154	$86.82	$86.80	$86.80
Purchase #5	$111.43	4.706%	$116.6739	$116.67	$116.65	$116.70
Purchase #6	$115.35	4.662%	$120.7276	$120.73	$120.75	$120.70
Purchase #7	$6.95	5.712%	$7.347	$7.35	$7.35	$7.30
7 purchase totals =	$542.95		$582.1605	$582.16	$582.15	$582.10