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	$82.34	7.361%	$88.401	$88.40	$88.40	$88.40
Purchase #2	$151.89	11.742%	$169.7249	$169.72	$169.70	$169.70
Purchase #3	$40.65	4.144%	$42.3345	$42.33	$42.35	$42.30
Purchase #4	$230.38	8.460%	$249.8701	$249.87	$249.85	$249.90
Purchase #5	$163.75	11.155%	$182.0163	$182.02	$182.00	$182.00
Purchase #6	$24.59	12.426%	$27.6456	$27.65	$27.65	$27.60
Purchase #7	$215.73	7.261%	$231.3942	$231.39	$231.40	$231.40
7 purchase totals =	$909.33		$991.3866	$991.38	$991.35	$991.30