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	$44.94	5.676%	$47.4908	$47.49	$47.50	$47.50
Purchase #2	$42.54	12.511%	$47.8622	$47.86	$47.85	$47.90
Purchase #3	$160.67	4.367%	$167.6865	$167.69	$167.70	$167.70
Purchase #4	$176.89	13.127%	$200.1104	$200.11	$200.10	$200.10
Purchase #5	$130.46	12.437%	$146.6853	$146.69	$146.70	$146.70
Purchase #6	$82.77	4.760%	$86.7099	$86.71	$86.70	$86.70
Purchase #7	$113.26	9.746%	$124.2983	$124.30	$124.30	$124.30
7 purchase totals =	$751.53		$820.8434	$820.85	$820.85	$820.90