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	$249.50	9.630%	$273.5269	$273.53	$273.55	$273.50
Purchase #2	$200.99	10.692%	$222.4799	$222.48	$222.50	$222.50
Purchase #3	$83.46	9.362%	$91.2735	$91.27	$91.25	$91.30
Purchase #4	$46.28	5.427%	$48.7916	$48.79	$48.80	$48.80
Purchase #5	$62.77	13.507%	$71.2483	$71.25	$71.25	$71.20
Purchase #6	$59.98	10.232%	$66.1172	$66.12	$66.10	$66.10
Purchase #7	$137.71	3.676%	$142.7722	$142.77	$142.75	$142.80
7 purchase totals =	$840.69		$916.2096	$916.21	$916.20	$916.20