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	$29.43	8.311%	$31.8759	$31.88	$31.90	$31.90
Purchase #2	$190.58	9.840%	$209.3331	$209.33	$209.35	$209.30
Purchase #3	$34.97	4.336%	$36.4863	$36.49	$36.50	$36.50
Purchase #4	$140.85	10.798%	$156.059	$156.06	$156.05	$156.10
Purchase #5	$209.38	4.180%	$218.1321	$218.13	$218.15	$218.10
Purchase #6	$64.56	7.710%	$69.5376	$69.54	$69.55	$69.50
Purchase #7	$92.82	6.632%	$98.9758	$98.98	$99.00	$99.00
7 purchase totals =	$762.59		$820.3998	$820.41	$820.50	$820.40