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	$90.74	9.561%	$99.4157	$99.42	$99.40	$99.40
Purchase #2	$190.27	11.303%	$211.7762	$211.78	$211.80	$211.80
Purchase #3	$208.42	11.344%	$232.0632	$232.06	$232.05	$232.10
Purchase #4	$73.39	7.799%	$79.1137	$79.11	$79.10	$79.10
Purchase #5	$49.90	13.794%	$56.7832	$56.78	$56.80	$56.80
Purchase #6	$123.50	3.655%	$128.0139	$128.01	$128.00	$128.00
Purchase #7	$65.40	11.443%	$72.8837	$72.88	$72.90	$72.90
7 purchase totals =	$801.62		$880.0496	$880.04	$880.05	$880.10