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	$30.66	7.842%	$33.0644	$33.06	$33.05	$33.10
Purchase #2	$96.57	10.311%	$106.5273	$106.53	$106.55	$106.50
Purchase #3	$80.98	6.618%	$86.3393	$86.34	$86.35	$86.30
Purchase #4	$250.71	4.133%	$261.0718	$261.07	$261.05	$261.10
Purchase #5	$171.96	5.795%	$181.9251	$181.93	$181.95	$181.90
Purchase #6	$194.59	5.566%	$205.4209	$205.42	$205.40	$205.40
Purchase #7	$123.83	6.197%	$131.5037	$131.50	$131.50	$131.50
7 purchase totals =	$949.30		$1,005.8525	$1,005.85	$1,005.85	$1,005.80