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	$154.48	6.257%	$164.1458	$164.15	$164.15	$164.10
Purchase #2	$156.73	7.760%	$168.8922	$168.89	$168.90	$168.90
Purchase #3	$163.50	7.694%	$176.0797	$176.08	$176.10	$176.10
Purchase #4	$73.49	5.222%	$77.3276	$77.33	$77.35	$77.30
Purchase #5	$83.71	8.585%	$90.8965	$90.90	$90.90	$90.90
Purchase #6	$187.80	3.359%	$194.1082	$194.11	$194.10	$194.10
Purchase #7	$234.63	6.141%	$249.0386	$249.04	$249.05	$249.00
7 purchase totals =	$1,054.34		$1,120.4886	$1,120.50	$1,120.55	$1,120.40