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	$140.93	13.251%	$159.6046	$159.60	$159.60	$159.60
Purchase #2	$125.98	4.645%	$131.8318	$131.83	$131.85	$131.80
Purchase #3	$31.26	7.340%	$33.5545	$33.55	$33.55	$33.60
Purchase #4	$240.40	3.743%	$249.3982	$249.40	$249.40	$249.40
Purchase #5	$164.48	12.835%	$185.591	$185.59	$185.60	$185.60
Purchase #6	$216.72	11.270%	$241.1443	$241.14	$241.15	$241.10
Purchase #7	$164.93	13.623%	$187.3984	$187.40	$187.40	$187.40
7 purchase totals =	$1,084.70		$1,188.5228	$1,188.51	$1,188.55	$1,188.50