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	$65.44	9.217%	$71.4716	$71.47	$71.45	$71.50
Purchase #2	$100.63	10.598%	$111.2948	$111.29	$111.30	$111.30
Purchase #3	$125.48	11.864%	$140.3669	$140.37	$140.35	$140.40
Purchase #4	$135.96	3.624%	$140.8872	$140.89	$140.90	$140.90
Purchase #5	$185.88	12.819%	$209.708	$209.71	$209.70	$209.70
Purchase #6	$128.74	13.349%	$145.9255	$145.93	$145.95	$145.90
Purchase #7	$84.38	5.858%	$89.323	$89.32	$89.30	$89.30
7 purchase totals =	$826.51		$908.9770	$908.98	$908.95	$909.00