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	$103.26	3.402%	$106.7729	$106.77	$106.75	$106.80
Purchase #2	$8.90	6.526%	$9.4808	$9.48	$9.50	$9.50
Purchase #3	$162.65	5.632%	$171.8104	$171.81	$171.80	$171.80
Purchase #4	$71.44	9.716%	$78.3811	$78.38	$78.40	$78.40
Purchase #5	$20.60	9.751%	$22.6087	$22.61	$22.60	$22.60
Purchase #6	$185.32	3.551%	$191.9007	$191.90	$191.90	$191.90
Purchase #7	$78.61	9.725%	$86.2548	$86.25	$86.25	$86.30
7 purchase totals =	$630.78		$667.2094	$667.20	$667.20	$667.30