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	$40.87	4.772%	$42.8203	$42.82	$42.80	$42.80
Purchase #2	$118.61	9.617%	$130.0167	$130.02	$130.00	$130.00
Purchase #3	$40.39	12.312%	$45.3628	$45.36	$45.35	$45.40
Purchase #4	$240.42	12.311%	$270.0181	$270.02	$270.00	$270.00
Purchase #5	$142.94	9.492%	$156.5079	$156.51	$156.50	$156.50
Purchase #6	$6.25	4.280%	$6.5175	$6.52	$6.50	$6.50
Purchase #7	$204.48	10.419%	$225.7848	$225.78	$225.80	$225.80
7 purchase totals =	$793.96		$877.0281	$877.03	$876.95	$877.00