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	$123.91	6.133%	$131.5094	$131.51	$131.50	$131.50
Purchase #2	$249.30	12.506%	$280.4775	$280.48	$280.50	$280.50
Purchase #3	$110.79	3.733%	$114.9258	$114.93	$114.95	$114.90
Purchase #4	$92.44	4.364%	$96.4741	$96.47	$96.45	$96.50
Purchase #5	$64.95	6.664%	$69.2783	$69.28	$69.30	$69.30
Purchase #6	$190.94	11.184%	$212.2947	$212.29	$212.30	$212.30
Purchase #7	$67.64	13.842%	$77.0027	$77.00	$77.00	$77.00
7 purchase totals =	$899.97		$981.9625	$981.96	$982.00	$982.00