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	$7.47	10.645%	$8.2652	$8.27	$8.25	$8.30
Purchase #2	$127.75	9.374%	$139.7253	$139.73	$139.75	$139.70
Purchase #3	$75.45	9.319%	$82.4812	$82.48	$82.50	$82.50
Purchase #4	$42.70	4.514%	$44.6275	$44.63	$44.65	$44.60
Purchase #5	$17.32	6.474%	$18.4413	$18.44	$18.45	$18.40
Purchase #6	$78.34	5.122%	$82.3526	$82.35	$82.35	$82.40
Purchase #7	$229.78	3.799%	$238.5093	$238.51	$238.50	$238.50
7 purchase totals =	$578.81		$614.4024	$614.41	$614.45	$614.40