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	$64.41	11.507%	$71.8217	$71.82	$71.80	$71.80
Purchase #2	$203.54	7.524%	$218.8543	$218.85	$218.85	$218.90
Purchase #3	$248.63	7.221%	$266.5836	$266.58	$266.60	$266.60
Purchase #4	$86.44	9.271%	$94.4539	$94.45	$94.45	$94.50
Purchase #5	$191.46	8.818%	$208.3429	$208.34	$208.35	$208.30
Purchase #6	$61.34	9.481%	$67.1556	$67.16	$67.15	$67.20
Purchase #7	$48.50	8.692%	$52.7156	$52.72	$52.70	$52.70
7 purchase totals =	$904.32		$979.9276	$979.92	$979.90	$980.00