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	$40.38	3.747%	$41.893	$41.89	$41.90	$41.90
Purchase #2	$219.53	3.135%	$226.4123	$226.41	$226.40	$226.40
Purchase #3	$38.99	6.663%	$41.5879	$41.59	$41.60	$41.60
Purchase #4	$23.31	7.689%	$25.1023	$25.10	$25.10	$25.10
Purchase #5	$103.95	5.357%	$109.5186	$109.52	$109.50	$109.50
Purchase #6	$239.72	10.180%	$264.1235	$264.12	$264.10	$264.10
Purchase #7	$102.96	6.143%	$109.2848	$109.28	$109.30	$109.30
7 purchase totals =	$768.84		$817.9224	$817.91	$817.90	$817.90