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	$121.56	10.512%	$134.3384	$134.34	$134.35	$134.30
Purchase #2	$82.53	12.495%	$92.8421	$92.84	$92.85	$92.80
Purchase #3	$181.76	6.676%	$193.8943	$193.89	$193.90	$193.90
Purchase #4	$20.32	6.667%	$21.6747	$21.67	$21.65	$21.70
Purchase #5	$79.48	13.393%	$90.1248	$90.12	$90.10	$90.10
Purchase #6	$249.90	12.200%	$280.3878	$280.39	$280.40	$280.40
Purchase #7	$174.73	6.368%	$185.8568	$185.86	$185.85	$185.90
7 purchase totals =	$910.28		$999.1189	$999.11	$999.10	$999.10