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	$28.35	11.352%	$31.5683	$31.57	$31.55	$31.60
Purchase #2	$61.41	3.518%	$63.5704	$63.57	$63.55	$63.60
Purchase #3	$90.34	5.739%	$95.5246	$95.52	$95.50	$95.50
Purchase #4	$154.83	5.184%	$162.8564	$162.86	$162.85	$162.90
Purchase #5	$92.65	4.337%	$96.6682	$96.67	$96.65	$96.70
Purchase #6	$45.63	3.508%	$47.2307	$47.23	$47.25	$47.20
Purchase #7	$88.88	10.404%	$98.1271	$98.13	$98.15	$98.10
7 purchase totals =	$562.09		$595.5457	$595.55	$595.50	$595.60