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	$156.51	8.288%	$169.4815	$169.48	$169.50	$169.50
Purchase #2	$90.97	9.788%	$99.8741	$99.87	$99.85	$99.90
Purchase #3	$188.30	13.158%	$213.0765	$213.08	$213.10	$213.10
Purchase #4	$79.89	12.632%	$89.9817	$89.98	$90.00	$90.00
Purchase #5	$250.78	9.238%	$273.9471	$273.95	$273.95	$273.90
Purchase #6	$193.83	7.510%	$208.3866	$208.39	$208.40	$208.40
Purchase #7	$147.31	7.744%	$158.7177	$158.72	$158.70	$158.70
7 purchase totals =	$1,107.59		$1,213.4652	$1,213.47	$1,213.50	$1,213.50