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	$223.43	12.270%	$250.8449	$250.84	$250.85	$250.80
Purchase #2	$183.78	10.528%	$203.1284	$203.13	$203.15	$203.10
Purchase #3	$82.39	11.534%	$91.8929	$91.89	$91.90	$91.90
Purchase #4	$222.27	9.577%	$243.5568	$243.56	$243.55	$243.60
Purchase #5	$153.99	8.830%	$167.5873	$167.59	$167.60	$167.60
Purchase #6	$51.97	10.702%	$57.5318	$57.53	$57.55	$57.50
Purchase #7	$29.50	6.586%	$31.4429	$31.44	$31.45	$31.40
7 purchase totals =	$947.33		$1,045.9850	$1,045.98	$1,046.05	$1,045.90