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	$39.33	6.841%	$42.0206	$42.02	$42.00	$42.00
Purchase #2	$23.56	5.408%	$24.8341	$24.83	$24.85	$24.80
Purchase #3	$157.51	7.623%	$169.517	$169.52	$169.50	$169.50
Purchase #4	$30.25	4.148%	$31.5048	$31.50	$31.50	$31.50
Purchase #5	$159.77	6.236%	$169.7333	$169.73	$169.75	$169.70
Purchase #6	$85.33	5.508%	$90.03	$90.03	$90.05	$90.00
Purchase #7	$229.89	8.800%	$250.1203	$250.12	$250.10	$250.10
7 purchase totals =	$725.64		$777.7601	$777.75	$777.75	$777.60