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	$112.55	10.621%	$124.5039	$124.50	$124.50	$124.50
Purchase #2	$125.69	13.371%	$142.496	$142.50	$142.50	$142.50
Purchase #3	$73.69	6.504%	$78.4828	$78.48	$78.50	$78.50
Purchase #4	$39.67	10.519%	$43.8429	$43.84	$43.85	$43.80
Purchase #5	$91.57	9.643%	$100.4001	$100.40	$100.40	$100.40
Purchase #6	$163.86	8.199%	$177.2949	$177.29	$177.30	$177.30
Purchase #7	$191.28	11.299%	$212.8927	$212.89	$212.90	$212.90
7 purchase totals =	$798.31		$879.9133	$879.90	$879.95	$879.90