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	$139.47	13.505%	$158.3054	$158.31	$158.30	$158.30
Purchase #2	$26.86	7.398%	$28.8471	$28.85	$28.85	$28.80
Purchase #3	$225.73	8.541%	$245.0096	$245.01	$245.00	$245.00
Purchase #4	$232.63	6.731%	$248.2883	$248.29	$248.30	$248.30
Purchase #5	$74.48	5.379%	$78.4863	$78.49	$78.50	$78.50
Purchase #6	$79.82	9.558%	$87.4492	$87.45	$87.45	$87.40
Purchase #7	$113.34	13.396%	$128.523	$128.52	$128.50	$128.50
7 purchase totals =	$892.33		$974.9089	$974.92	$974.90	$974.80