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	$36.35	11.256%	$40.4416	$40.44	$40.45	$40.40
Purchase #2	$161.49	11.109%	$179.4299	$179.43	$179.45	$179.40
Purchase #3	$94.82	9.799%	$104.1114	$104.11	$104.10	$104.10
Purchase #4	$31.54	7.366%	$33.8632	$33.86	$33.85	$33.90
Purchase #5	$93.78	3.283%	$96.8588	$96.86	$96.85	$96.90
Purchase #6	$47.66	9.508%	$52.1915	$52.19	$52.20	$52.20
Purchase #7	$41.58	5.306%	$43.7862	$43.79	$43.80	$43.80
7 purchase totals =	$507.22		$550.6826	$550.68	$550.70	$550.70