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	$124.79	5.707%	$131.9118	$131.91	$131.90	$131.90
Purchase #2	$119.42	3.394%	$123.4731	$123.47	$123.45	$123.50
Purchase #3	$46.96	13.561%	$53.3282	$53.33	$53.35	$53.30
Purchase #4	$134.83	5.737%	$142.5652	$142.57	$142.55	$142.60
Purchase #5	$32.53	11.398%	$36.2378	$36.24	$36.25	$36.20
Purchase #6	$193.80	10.352%	$213.8622	$213.86	$213.85	$213.90
Purchase #7	$151.30	11.654%	$168.9325	$168.93	$168.95	$168.90
7 purchase totals =	$803.63		$870.3108	$870.31	$870.30	$870.30