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	$73.57	12.728%	$82.934	$82.93	$82.95	$82.90
Purchase #2	$83.48	4.675%	$87.3827	$87.38	$87.40	$87.40
Purchase #3	$137.84	9.355%	$150.7349	$150.73	$150.75	$150.70
Purchase #4	$199.55	10.424%	$220.3511	$220.35	$220.35	$220.40
Purchase #5	$33.86	13.385%	$38.3922	$38.39	$38.40	$38.40
Purchase #6	$96.63	9.579%	$105.8862	$105.89	$105.90	$105.90
Purchase #7	$50.84	12.796%	$57.3455	$57.35	$57.35	$57.30
7 purchase totals =	$675.77		$743.0266	$743.02	$743.10	$743.00