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	$76.79	6.104%	$81.4773	$81.48	$81.50	$81.50
Purchase #2	$93.49	13.324%	$105.9466	$105.95	$105.95	$105.90
Purchase #3	$63.62	12.437%	$71.5324	$71.53	$71.55	$71.50
Purchase #4	$170.86	9.751%	$187.5206	$187.52	$187.50	$187.50
Purchase #5	$69.86	11.851%	$78.1391	$78.14	$78.15	$78.10
Purchase #6	$246.76	8.614%	$268.0159	$268.02	$268.00	$268.00
Purchase #7	$207.53	5.816%	$219.5999	$219.60	$219.60	$219.60
7 purchase totals =	$928.91		$1,012.2318	$1,012.24	$1,012.25	$1,012.10