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	$45.59	12.612%	$51.3398	$51.34	$51.35	$51.30
Purchase #2	$53.96	3.393%	$55.7909	$55.79	$55.80	$55.80
Purchase #3	$249.28	13.275%	$282.3719	$282.37	$282.35	$282.40
Purchase #4	$146.97	10.835%	$162.8942	$162.89	$162.90	$162.90
Purchase #5	$75.33	10.648%	$83.3511	$83.35	$83.35	$83.40
Purchase #6	$178.43	9.607%	$195.5718	$195.57	$195.55	$195.60
Purchase #7	$94.57	4.254%	$98.593	$98.59	$98.60	$98.60
7 purchase totals =	$844.13		$929.9127	$929.90	$929.90	$930.00