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	$75.91	12.511%	$85.4071	$85.41	$85.40	$85.40
Purchase #2	$198.44	13.102%	$224.4396	$224.44	$224.45	$224.40
Purchase #3	$97.92	11.686%	$109.3629	$109.36	$109.35	$109.40
Purchase #4	$84.33	5.583%	$89.0381	$89.04	$89.05	$89.00
Purchase #5	$113.82	7.503%	$122.3599	$122.36	$122.35	$122.40
Purchase #6	$123.60	5.418%	$130.2966	$130.30	$130.30	$130.30
Purchase #7	$212.46	13.379%	$240.885	$240.89	$240.90	$240.90
7 purchase totals =	$906.48		$1,001.7892	$1,001.80	$1,001.80	$1,001.80