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	$84.55	5.580%	$89.2679	$89.27	$89.25	$89.30
Purchase #2	$151.94	8.443%	$164.7683	$164.77	$164.75	$164.80
Purchase #3	$72.56	8.454%	$78.6942	$78.69	$78.70	$78.70
Purchase #4	$90.34	8.533%	$98.0487	$98.05	$98.05	$98.00
Purchase #5	$84.90	12.611%	$95.6067	$95.61	$95.60	$95.60
Purchase #6	$149.90	3.656%	$155.3803	$155.38	$155.40	$155.40
Purchase #7	$161.91	11.203%	$180.0488	$180.05	$180.05	$180.00
7 purchase totals =	$796.10		$861.8149	$861.82	$861.80	$861.80