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	$67.93	5.835%	$71.8937	$71.89	$71.90	$71.90
Purchase #2	$79.91	12.127%	$89.6007	$89.60	$89.60	$89.60
Purchase #3	$137.44	13.821%	$156.4356	$156.44	$156.45	$156.40
Purchase #4	$214.60	7.270%	$230.2014	$230.20	$230.20	$230.20
Purchase #5	$87.76	6.267%	$93.2599	$93.26	$93.25	$93.30
Purchase #6	$243.56	8.128%	$263.3566	$263.36	$263.35	$263.40
Purchase #7	$180.42	8.639%	$196.0065	$196.01	$196.00	$196.00
7 purchase totals =	$1,011.62		$1,100.7544	$1,100.76	$1,100.75	$1,100.80