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	$160.69	13.212%	$181.9204	$181.92	$181.90	$181.90
Purchase #2	$92.34	6.350%	$98.2036	$98.20	$98.20	$98.20
Purchase #3	$170.30	10.629%	$188.4012	$188.40	$188.40	$188.40
Purchase #4	$150.29	4.373%	$156.8622	$156.86	$156.85	$156.90
Purchase #5	$37.83	5.471%	$39.8997	$39.90	$39.90	$39.90
Purchase #6	$22.73	7.699%	$24.48	$24.48	$24.50	$24.50
Purchase #7	$157.47	6.751%	$168.1008	$168.10	$168.10	$168.10
7 purchase totals =	$791.65		$857.8679	$857.86	$857.85	$857.90