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	$43.80	6.239%	$46.5327	$46.53	$46.55	$46.50
Purchase #2	$80.71	11.633%	$90.099	$90.10	$90.10	$90.10
Purchase #3	$141.57	13.128%	$160.1553	$160.16	$160.15	$160.20
Purchase #4	$64.46	8.402%	$69.8759	$69.88	$69.90	$69.90
Purchase #5	$207.77	6.754%	$221.8028	$221.80	$221.80	$221.80
Purchase #6	$103.26	3.490%	$106.8638	$106.86	$106.85	$106.90
Purchase #7	$89.95	7.303%	$96.519	$96.52	$96.50	$96.50
7 purchase totals =	$731.52		$791.8485	$791.85	$791.85	$791.90