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	$137.36	3.553%	$142.2404	$142.24	$142.25	$142.20
Purchase #2	$54.48	8.680%	$59.2089	$59.21	$59.20	$59.20
Purchase #3	$29.90	5.514%	$31.5487	$31.55	$31.55	$31.50
Purchase #4	$174.76	7.856%	$188.4891	$188.49	$188.50	$188.50
Purchase #5	$202.46	10.241%	$223.1939	$223.19	$223.20	$223.20
Purchase #6	$159.29	4.507%	$166.4692	$166.47	$166.45	$166.50
Purchase #7	$49.48	8.629%	$53.7496	$53.75	$53.75	$53.70
7 purchase totals =	$807.73		$864.8998	$864.90	$864.90	$864.80