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	$7.83	5.644%	$8.2719	$8.27	$8.25	$8.30
Purchase #2	$236.45	13.469%	$268.2975	$268.30	$268.30	$268.30
Purchase #3	$128.82	5.241%	$135.5715	$135.57	$135.55	$135.60
Purchase #4	$100.84	12.727%	$113.6739	$113.67	$113.65	$113.70
Purchase #5	$115.79	6.630%	$123.4669	$123.47	$123.45	$123.50
Purchase #6	$72.79	13.375%	$82.5257	$82.53	$82.55	$82.50
Purchase #7	$126.37	13.672%	$143.6473	$143.65	$143.65	$143.60
7 purchase totals =	$788.89		$875.4547	$875.46	$875.40	$875.50