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	$81.37	9.303%	$88.9399	$88.94	$88.95	$88.90
Purchase #2	$219.47	9.584%	$240.504	$240.50	$240.50	$240.50
Purchase #3	$234.51	12.781%	$264.4827	$264.48	$264.50	$264.50
Purchase #4	$55.98	10.264%	$61.7258	$61.73	$61.75	$61.70
Purchase #5	$105.54	8.857%	$114.8877	$114.89	$114.90	$114.90
Purchase #6	$11.50	5.616%	$12.1458	$12.15	$12.15	$12.10
Purchase #7	$63.72	11.303%	$70.9223	$70.92	$70.90	$70.90
7 purchase totals =	$772.09		$853.6082	$853.61	$853.65	$853.50