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	$47.71	6.639%	$50.8775	$50.88	$50.90	$50.90
Purchase #2	$40.39	8.630%	$43.8757	$43.88	$43.90	$43.90
Purchase #3	$225.34	11.338%	$250.889	$250.89	$250.90	$250.90
Purchase #4	$243.81	13.169%	$275.9173	$275.92	$275.90	$275.90
Purchase #5	$247.77	5.571%	$261.5733	$261.57	$261.55	$261.60
Purchase #6	$46.39	6.216%	$49.2736	$49.27	$49.25	$49.30
Purchase #7	$95.33	3.847%	$98.9973	$99.00	$99.00	$99.00
7 purchase totals =	$946.74		$1,031.4037	$1,031.41	$1,031.40	$1,031.50