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	$80.52	12.503%	$90.5874	$90.59	$90.60	$90.60
Purchase #2	$27.58	12.304%	$30.9734	$30.97	$30.95	$31.00
Purchase #3	$189.98	5.552%	$200.5277	$200.53	$200.55	$200.50
Purchase #4	$45.46	4.145%	$47.3443	$47.34	$47.35	$47.30
Purchase #5	$142.61	3.872%	$148.1319	$148.13	$148.15	$148.10
Purchase #6	$12.36	12.288%	$13.8788	$13.88	$13.90	$13.90
Purchase #7	$154.64	8.506%	$167.7937	$167.79	$167.80	$167.80
7 purchase totals =	$653.15		$699.2372	$699.23	$699.30	$699.20