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	$126.39	4.269%	$131.7856	$131.79	$131.80	$131.80
Purchase #2	$190.58	13.674%	$216.6399	$216.64	$216.65	$216.60
Purchase #3	$237.59	12.858%	$268.1393	$268.14	$268.15	$268.10
Purchase #4	$41.59	4.372%	$43.4083	$43.41	$43.40	$43.40
Purchase #5	$167.50	6.432%	$178.2736	$178.27	$178.25	$178.30
Purchase #6	$179.83	4.744%	$188.3611	$188.36	$188.35	$188.40
Purchase #7	$11.84	11.855%	$13.2436	$13.24	$13.25	$13.20
7 purchase totals =	$955.32		$1,039.8514	$1,039.85	$1,039.85	$1,039.80