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	$84.37	7.268%	$90.502	$90.50	$90.50	$90.50
Purchase #2	$153.56	12.484%	$172.7304	$172.73	$172.75	$172.70
Purchase #3	$81.27	9.592%	$89.0654	$89.07	$89.05	$89.10
Purchase #4	$162.43	5.503%	$171.3685	$171.37	$171.35	$171.40
Purchase #5	$114.62	8.496%	$124.3581	$124.36	$124.35	$124.40
Purchase #6	$114.97	11.650%	$128.364	$128.36	$128.35	$128.40
Purchase #7	$132.89	11.265%	$147.8601	$147.86	$147.85	$147.90
7 purchase totals =	$844.11		$924.2485	$924.25	$924.20	$924.40