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	$20.46	10.178%	$22.5424	$22.54	$22.55	$22.50
Purchase #2	$64.80	8.515%	$70.3177	$70.32	$70.30	$70.30
Purchase #3	$85.30	6.199%	$90.5877	$90.59	$90.60	$90.60
Purchase #4	$176.79	12.490%	$198.8711	$198.87	$198.85	$198.90
Purchase #5	$223.53	8.543%	$242.6262	$242.63	$242.65	$242.60
Purchase #6	$162.69	13.629%	$184.863	$184.86	$184.85	$184.90
Purchase #7	$209.76	11.368%	$233.6055	$233.61	$233.60	$233.60
7 purchase totals =	$943.33		$1,043.4136	$1,043.42	$1,043.40	$1,043.40