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	$63.54	12.172%	$71.2741	$71.27	$71.25	$71.30
Purchase #2	$157.67	8.489%	$171.0546	$171.05	$171.05	$171.10
Purchase #3	$126.88	8.694%	$137.9109	$137.91	$137.90	$137.90
Purchase #4	$99.85	4.319%	$104.1625	$104.16	$104.15	$104.20
Purchase #5	$32.35	4.450%	$33.7896	$33.79	$33.80	$33.80
Purchase #6	$119.48	7.531%	$128.478	$128.48	$128.50	$128.50
Purchase #7	$225.35	3.556%	$233.3634	$233.36	$233.35	$233.40
7 purchase totals =	$825.12		$880.0331	$880.02	$880.00	$880.20