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	$30.40	3.380%	$31.4275	$31.43	$31.45	$31.40
Purchase #2	$92.91	5.868%	$98.362	$98.36	$98.35	$98.40
Purchase #3	$245.61	5.609%	$259.3863	$259.39	$259.40	$259.40
Purchase #4	$91.49	4.435%	$95.5476	$95.55	$95.55	$95.50
Purchase #5	$228.96	9.446%	$250.5876	$250.59	$250.60	$250.60
Purchase #6	$27.51	3.826%	$28.5625	$28.56	$28.55	$28.60
Purchase #7	$22.44	13.272%	$25.4182	$25.42	$25.40	$25.40
7 purchase totals =	$739.32		$789.2917	$789.30	$789.30	$789.30