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	$138.85	7.228%	$148.8861	$148.89	$148.90	$148.90
Purchase #2	$134.96	9.264%	$147.4627	$147.46	$147.45	$147.50
Purchase #3	$30.60	3.230%	$31.5884	$31.59	$31.60	$31.60
Purchase #4	$64.94	3.829%	$67.4266	$67.43	$67.45	$67.40
Purchase #5	$167.32	10.129%	$184.2678	$184.27	$184.25	$184.30
Purchase #6	$39.35	4.421%	$41.0897	$41.09	$41.10	$41.10
Purchase #7	$158.53	12.834%	$178.8757	$178.88	$178.90	$178.90
7 purchase totals =	$734.55		$799.5970	$799.61	$799.65	$799.70