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	$247.36	13.546%	$280.8674	$280.87	$280.85	$280.90
Purchase #2	$63.73	9.698%	$69.9105	$69.91	$69.90	$69.90
Purchase #3	$41.51	3.156%	$42.8201	$42.82	$42.80	$42.80
Purchase #4	$152.43	12.373%	$171.2902	$171.29	$171.30	$171.30
Purchase #5	$248.81	7.392%	$267.202	$267.20	$267.20	$267.20
Purchase #6	$147.82	13.866%	$168.3167	$168.32	$168.30	$168.30
Purchase #7	$35.32	4.457%	$36.8942	$36.89	$36.90	$36.90
7 purchase totals =	$936.98		$1,037.3011	$1,037.30	$1,037.25	$1,037.30