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	$209.41	10.413%	$231.2159	$231.22	$231.20	$231.20
Purchase #2	$245.44	11.736%	$274.2448	$274.24	$274.25	$274.20
Purchase #3	$134.73	3.418%	$139.3351	$139.34	$139.35	$139.30
Purchase #4	$28.89	9.851%	$31.736	$31.74	$31.75	$31.70
Purchase #5	$49.59	13.641%	$56.3546	$56.35	$56.35	$56.40
Purchase #6	$24.82	13.869%	$28.2623	$28.26	$28.25	$28.30
Purchase #7	$72.28	8.550%	$78.4599	$78.46	$78.45	$78.50
7 purchase totals =	$765.16		$839.6086	$839.61	$839.60	$839.60