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	$73.79	6.449%	$78.5487	$78.55	$78.55	$78.50
Purchase #2	$140.98	10.582%	$155.8985	$155.90	$155.90	$155.90
Purchase #3	$118.71	3.116%	$122.409	$122.41	$122.40	$122.40
Purchase #4	$153.31	11.733%	$171.2979	$171.30	$171.30	$171.30
Purchase #5	$168.94	8.846%	$183.8844	$183.88	$183.90	$183.90
Purchase #6	$33.79	13.872%	$38.4773	$38.48	$38.50	$38.50
Purchase #7	$222.44	10.460%	$245.7072	$245.71	$245.70	$245.70
7 purchase totals =	$911.96		$996.2230	$996.23	$996.25	$996.20