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	$131.91	6.865%	$140.9656	$140.97	$140.95	$141.00
Purchase #2	$94.57	12.192%	$106.1	$106.10	$106.10	$106.10
Purchase #3	$94.41	9.261%	$103.1533	$103.15	$103.15	$103.20
Purchase #4	$119.25	3.253%	$123.1292	$123.13	$123.15	$123.10
Purchase #5	$236.90	10.555%	$261.9048	$261.90	$261.90	$261.90
Purchase #6	$84.57	7.129%	$90.599	$90.60	$90.60	$90.60
Purchase #7	$5.90	10.662%	$6.5291	$6.53	$6.55	$6.50
7 purchase totals =	$767.51		$832.3810	$832.38	$832.40	$832.40