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	$243.55	11.117%	$270.6255	$270.63	$270.65	$270.60
Purchase #2	$90.65	9.861%	$99.589	$99.59	$99.60	$99.60
Purchase #3	$184.48	7.822%	$198.91	$198.91	$198.90	$198.90
Purchase #4	$86.83	5.844%	$91.9043	$91.90	$91.90	$91.90
Purchase #5	$174.46	9.413%	$190.8819	$190.88	$190.90	$190.90
Purchase #6	$170.56	6.181%	$181.1023	$181.10	$181.10	$181.10
Purchase #7	$203.48	12.797%	$229.5193	$229.52	$229.50	$229.50
7 purchase totals =	$1,154.01		$1,262.5323	$1,262.53	$1,262.55	$1,262.50