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	$136.95	4.275%	$142.8046	$142.80	$142.80	$142.80
Purchase #2	$165.31	10.217%	$182.1997	$182.20	$182.20	$182.20
Purchase #3	$52.61	13.641%	$59.7865	$59.79	$59.80	$59.80
Purchase #4	$139.44	12.834%	$157.3357	$157.34	$157.35	$157.30
Purchase #5	$95.73	13.364%	$108.5234	$108.52	$108.50	$108.50
Purchase #6	$104.37	4.515%	$109.0823	$109.08	$109.10	$109.10
Purchase #7	$29.90	8.216%	$32.3566	$32.36	$32.35	$32.40
7 purchase totals =	$724.31		$792.0888	$792.09	$792.10	$792.10