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	$43.73	12.331%	$49.1223	$49.12	$49.10	$49.10
Purchase #2	$78.38	6.282%	$83.3038	$83.30	$83.30	$83.30
Purchase #3	$240.58	9.540%	$263.5313	$263.53	$263.55	$263.50
Purchase #4	$156.56	7.257%	$167.9216	$167.92	$167.90	$167.90
Purchase #5	$166.74	9.662%	$182.8504	$182.85	$182.85	$182.90
Purchase #6	$17.42	5.778%	$18.4265	$18.43	$18.45	$18.40
Purchase #7	$18.74	3.770%	$19.4465	$19.45	$19.45	$19.40
7 purchase totals =	$722.15		$784.6024	$784.60	$784.60	$784.50