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	$105.91	3.695%	$109.8234	$109.82	$109.80	$109.80
Purchase #2	$94.71	5.701%	$100.1094	$100.11	$100.10	$100.10
Purchase #3	$51.67	10.392%	$57.0395	$57.04	$57.05	$57.00
Purchase #4	$89.28	13.860%	$101.6542	$101.65	$101.65	$101.70
Purchase #5	$189.34	6.848%	$202.306	$202.31	$202.30	$202.30
Purchase #6	$189.69	3.835%	$196.9646	$196.96	$196.95	$197.00
Purchase #7	$134.78	9.811%	$148.0033	$148.00	$148.00	$148.00
7 purchase totals =	$855.38		$915.9004	$915.89	$915.85	$915.90