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	$30.35	4.250%	$31.6399	$31.64	$31.65	$31.60
Purchase #2	$198.67	6.621%	$211.8239	$211.82	$211.80	$211.80
Purchase #3	$188.90	11.764%	$211.1222	$211.12	$211.10	$211.10
Purchase #4	$140.96	3.477%	$145.8612	$145.86	$145.85	$145.90
Purchase #5	$114.61	7.803%	$123.553	$123.55	$123.55	$123.60
Purchase #6	$112.38	6.227%	$119.3779	$119.38	$119.40	$119.40
Purchase #7	$201.81	8.787%	$219.543	$219.54	$219.55	$219.50
7 purchase totals =	$987.68		$1,062.9211	$1,062.91	$1,062.90	$1,062.90