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	$6.69	11.804%	$7.4797	$7.48	$7.50	$7.50
Purchase #2	$230.41	8.304%	$249.5432	$249.54	$249.55	$249.50
Purchase #3	$113.85	8.240%	$123.2312	$123.23	$123.25	$123.20
Purchase #4	$82.41	4.445%	$86.0731	$86.07	$86.05	$86.10
Purchase #5	$69.82	9.658%	$76.5632	$76.56	$76.55	$76.60
Purchase #6	$179.93	10.282%	$198.4304	$198.43	$198.45	$198.40
Purchase #7	$162.25	5.507%	$171.1851	$171.19	$171.20	$171.20
7 purchase totals =	$845.36		$912.5059	$912.50	$912.55	$912.50