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	$94.31	6.375%	$100.3223	$100.32	$100.30	$100.30
Purchase #2	$27.39	9.328%	$29.9449	$29.94	$29.95	$29.90
Purchase #3	$223.79	9.702%	$245.5021	$245.50	$245.50	$245.50
Purchase #4	$182.36	13.116%	$206.2783	$206.28	$206.30	$206.30
Purchase #5	$136.79	3.682%	$141.8266	$141.83	$141.85	$141.80
Purchase #6	$42.72	13.212%	$48.3642	$48.36	$48.35	$48.40
Purchase #7	$53.47	4.192%	$55.7115	$55.71	$55.70	$55.70
7 purchase totals =	$760.83		$827.9499	$827.94	$827.95	$827.90