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	$143.34	8.193%	$155.0838	$155.08	$155.10	$155.10
Purchase #2	$234.56	10.804%	$259.9019	$259.90	$259.90	$259.90
Purchase #3	$29.90	7.388%	$32.109	$32.11	$32.10	$32.10
Purchase #4	$131.35	11.813%	$146.8664	$146.87	$146.85	$146.90
Purchase #5	$35.42	12.595%	$39.8811	$39.88	$39.90	$39.90
Purchase #6	$147.73	3.216%	$152.481	$152.48	$152.50	$152.50
Purchase #7	$45.41	4.681%	$47.5356	$47.54	$47.55	$47.50
7 purchase totals =	$767.71		$833.8588	$833.86	$833.90	$833.90