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	$145.48	13.332%	$164.8754	$164.88	$164.90	$164.90
Purchase #2	$61.60	8.839%	$67.0448	$67.04	$67.05	$67.00
Purchase #3	$98.55	11.543%	$109.9256	$109.93	$109.95	$109.90
Purchase #4	$29.43	8.361%	$31.8906	$31.89	$31.90	$31.90
Purchase #5	$168.25	9.174%	$183.6853	$183.69	$183.70	$183.70
Purchase #6	$66.81	5.280%	$70.3376	$70.34	$70.35	$70.30
Purchase #7	$33.42	5.525%	$35.2665	$35.27	$35.25	$35.30
7 purchase totals =	$603.54		$663.0258	$663.04	$663.10	$663.00