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	$164.62	12.818%	$185.721	$185.72	$185.70	$185.70
Purchase #2	$85.38	4.869%	$89.5372	$89.54	$89.55	$89.50
Purchase #3	$41.88	10.702%	$46.362	$46.36	$46.35	$46.40
Purchase #4	$249.27	7.145%	$267.0803	$267.08	$267.10	$267.10
Purchase #5	$35.42	6.772%	$37.8186	$37.82	$37.80	$37.80
Purchase #6	$24.94	4.727%	$26.1189	$26.12	$26.10	$26.10
Purchase #7	$237.61	4.785%	$248.9796	$248.98	$249.00	$249.00
7 purchase totals =	$839.12		$901.6176	$901.62	$901.60	$901.60