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	$72.71	7.487%	$78.1538	$78.15	$78.15	$78.20
Purchase #2	$201.67	13.659%	$229.2161	$229.22	$229.20	$229.20
Purchase #3	$125.79	13.261%	$142.471	$142.47	$142.45	$142.50
Purchase #4	$213.63	4.296%	$222.8075	$222.81	$222.80	$222.80
Purchase #5	$32.93	10.180%	$36.2823	$36.28	$36.30	$36.30
Purchase #6	$49.76	12.372%	$55.9163	$55.92	$55.90	$55.90
Purchase #7	$63.25	9.259%	$69.1063	$69.11	$69.10	$69.10
7 purchase totals =	$759.74		$833.9533	$833.96	$833.90	$834.00