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	$113.83	6.588%	$121.3291	$121.33	$121.35	$121.30
Purchase #2	$10.48	12.398%	$11.7793	$11.78	$11.80	$11.80
Purchase #3	$54.43	9.208%	$59.4419	$59.44	$59.45	$59.40
Purchase #4	$108.30	8.267%	$117.2532	$117.25	$117.25	$117.30
Purchase #5	$30.43	11.367%	$33.889	$33.89	$33.90	$33.90
Purchase #6	$172.39	8.459%	$186.9725	$186.97	$186.95	$187.00
Purchase #7	$250.69	4.687%	$262.4398	$262.44	$262.45	$262.40
7 purchase totals =	$740.55		$793.1048	$793.10	$793.15	$793.10