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	$75.90	8.645%	$82.4616	$82.46	$82.45	$82.50
Purchase #2	$38.26	3.872%	$39.7414	$39.74	$39.75	$39.70
Purchase #3	$153.78	3.586%	$159.2946	$159.29	$159.30	$159.30
Purchase #4	$247.25	7.376%	$265.4872	$265.49	$265.50	$265.50
Purchase #5	$229.63	4.668%	$240.3491	$240.35	$240.35	$240.30
Purchase #6	$20.96	7.266%	$22.483	$22.48	$22.50	$22.50
Purchase #7	$90.79	9.162%	$99.1082	$99.11	$99.10	$99.10
7 purchase totals =	$856.57		$908.9251	$908.92	$908.95	$908.90