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	$25.40	10.664%	$28.1087	$28.11	$28.10	$28.10
Purchase #2	$195.38	13.515%	$221.7856	$221.79	$221.80	$221.80
Purchase #3	$78.85	9.589%	$86.4109	$86.41	$86.40	$86.40
Purchase #4	$210.43	5.841%	$222.7212	$222.72	$222.70	$222.70
Purchase #5	$99.63	4.219%	$103.8334	$103.83	$103.85	$103.80
Purchase #6	$134.39	5.246%	$141.4401	$141.44	$141.45	$141.40
Purchase #7	$21.30	7.465%	$22.89	$22.89	$22.90	$22.90
7 purchase totals =	$765.38		$827.1899	$827.19	$827.20	$827.10