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	$37.77	11.240%	$42.0153	$42.02	$42.00	$42.00
Purchase #2	$221.31	9.779%	$242.9519	$242.95	$242.95	$243.00
Purchase #3	$147.35	11.440%	$164.2068	$164.21	$164.20	$164.20
Purchase #4	$86.88	4.650%	$90.9199	$90.92	$90.90	$90.90
Purchase #5	$103.69	11.618%	$115.7367	$115.74	$115.75	$115.70
Purchase #6	$172.27	8.553%	$187.0043	$187.00	$187.00	$187.00
Purchase #7	$88.65	10.646%	$98.0877	$98.09	$98.10	$98.10
7 purchase totals =	$857.92		$940.9226	$940.93	$940.90	$940.90