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	$81.39	6.113%	$86.3654	$86.37	$86.35	$86.40
Purchase #2	$76.57	11.864%	$85.6543	$85.65	$85.65	$85.70
Purchase #3	$81.35	12.149%	$91.2332	$91.23	$91.25	$91.20
Purchase #4	$239.78	4.251%	$249.973	$249.97	$249.95	$250.00
Purchase #5	$55.66	10.560%	$61.5377	$61.54	$61.55	$61.50
Purchase #6	$42.99	10.538%	$47.5203	$47.52	$47.50	$47.50
Purchase #7	$156.59	7.453%	$168.2607	$168.26	$168.25	$168.30
7 purchase totals =	$734.33		$790.5446	$790.54	$790.50	$790.60