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	$43.70	11.423%	$48.6919	$48.69	$48.70	$48.70
Purchase #2	$38.59	13.824%	$43.9247	$43.92	$43.90	$43.90
Purchase #3	$167.89	12.808%	$189.3934	$189.39	$189.40	$189.40
Purchase #4	$248.90	12.700%	$280.5103	$280.51	$280.50	$280.50
Purchase #5	$175.70	7.359%	$188.6298	$188.63	$188.65	$188.60
Purchase #6	$96.84	13.289%	$109.7091	$109.71	$109.70	$109.70
Purchase #7	$108.76	9.740%	$119.3532	$119.35	$119.35	$119.40
7 purchase totals =	$880.38		$980.2124	$980.20	$980.20	$980.20