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	$44.91	13.312%	$50.8884	$50.89	$50.90	$50.90
Purchase #2	$245.96	3.208%	$253.8504	$253.85	$253.85	$253.90
Purchase #3	$47.94	9.227%	$52.3634	$52.36	$52.35	$52.40
Purchase #4	$196.27	4.183%	$204.48	$204.48	$204.50	$204.50
Purchase #5	$249.32	8.619%	$270.8089	$270.81	$270.80	$270.80
Purchase #6	$185.77	6.644%	$198.1126	$198.11	$198.10	$198.10
Purchase #7	$56.60	5.487%	$59.7056	$59.71	$59.70	$59.70
7 purchase totals =	$1,026.77		$1,090.2093	$1,090.21	$1,090.20	$1,090.30