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	$246.93	3.797%	$256.3059	$256.31	$256.30	$256.30
Purchase #2	$7.62	3.373%	$7.877	$7.88	$7.90	$7.90
Purchase #3	$118.58	5.816%	$125.4766	$125.48	$125.50	$125.50
Purchase #4	$132.44	10.858%	$146.8203	$146.82	$146.80	$146.80
Purchase #5	$94.66	11.578%	$105.6197	$105.62	$105.60	$105.60
Purchase #6	$96.67	10.805%	$107.1152	$107.12	$107.10	$107.10
Purchase #7	$132.37	13.780%	$150.6106	$150.61	$150.60	$150.60
7 purchase totals =	$829.27		$899.8253	$899.84	$899.80	$899.80