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	$25.35	5.744%	$26.8061	$26.81	$26.80	$26.80
Purchase #2	$19.53	6.470%	$20.7936	$20.79	$20.80	$20.80
Purchase #3	$151.58	11.381%	$168.8313	$168.83	$168.85	$168.80
Purchase #4	$185.35	5.693%	$195.902	$195.90	$195.90	$195.90
Purchase #5	$61.48	6.760%	$65.636	$65.64	$65.65	$65.60
Purchase #6	$186.48	12.417%	$209.6352	$209.64	$209.65	$209.60
Purchase #7	$168.69	6.536%	$179.7156	$179.72	$179.70	$179.70
7 purchase totals =	$798.46		$867.3198	$867.33	$867.35	$867.20