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	$161.88	3.830%	$168.08	$168.08	$168.10	$168.10
Purchase #2	$133.77	5.132%	$140.6351	$140.64	$140.65	$140.60
Purchase #3	$67.46	7.441%	$72.4797	$72.48	$72.50	$72.50
Purchase #4	$78.71	9.579%	$86.2496	$86.25	$86.25	$86.20
Purchase #5	$65.69	13.368%	$74.4714	$74.47	$74.45	$74.50
Purchase #6	$73.38	13.261%	$83.1109	$83.11	$83.10	$83.10
Purchase #7	$192.95	3.263%	$199.246	$199.25	$199.25	$199.20
7 purchase totals =	$773.84		$824.2727	$824.28	$824.30	$824.20