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	$131.78	12.314%	$148.0074	$148.01	$148.00	$148.00
Purchase #2	$225.54	5.506%	$237.9582	$237.96	$237.95	$238.00
Purchase #3	$75.26	8.430%	$81.6044	$81.60	$81.60	$81.60
Purchase #4	$196.42	9.641%	$215.3569	$215.36	$215.35	$215.40
Purchase #5	$81.64	10.394%	$90.1257	$90.13	$90.15	$90.10
Purchase #6	$91.88	12.742%	$103.5873	$103.59	$103.60	$103.60
Purchase #7	$84.42	9.644%	$92.5615	$92.56	$92.55	$92.60
7 purchase totals =	$886.94		$969.2014	$969.21	$969.20	$969.30