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	$71.63	13.616%	$81.3831	$81.38	$81.40	$81.40
Purchase #2	$198.96	6.813%	$212.5151	$212.52	$212.50	$212.50
Purchase #3	$143.51	9.102%	$156.5723	$156.57	$156.55	$156.60
Purchase #4	$82.40	9.661%	$90.3607	$90.36	$90.35	$90.40
Purchase #5	$90.89	9.301%	$99.3437	$99.34	$99.35	$99.30
Purchase #6	$215.69	4.152%	$224.6454	$224.65	$224.65	$224.60
Purchase #7	$96.71	11.791%	$108.1131	$108.11	$108.10	$108.10
7 purchase totals =	$899.79		$972.9334	$972.93	$972.90	$972.90