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	$81.46	9.571%	$89.2565	$89.26	$89.25	$89.30
Purchase #2	$228.51	8.721%	$248.4384	$248.44	$248.45	$248.40
Purchase #3	$91.72	8.483%	$99.5006	$99.50	$99.50	$99.50
Purchase #4	$66.80	7.199%	$71.6089	$71.61	$71.60	$71.60
Purchase #5	$86.40	8.669%	$93.89	$93.89	$93.90	$93.90
Purchase #6	$25.37	10.363%	$27.9991	$28.00	$28.00	$28.00
Purchase #7	$135.59	7.870%	$146.2609	$146.26	$146.25	$146.30
7 purchase totals =	$715.85		$776.9544	$776.96	$776.95	$777.00