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	$29.67	13.840%	$33.7763	$33.78	$33.80	$33.80
Purchase #2	$50.59	7.873%	$54.573	$54.57	$54.55	$54.60
Purchase #3	$166.52	11.237%	$185.2319	$185.23	$185.25	$185.20
Purchase #4	$243.26	13.424%	$275.9152	$275.92	$275.90	$275.90
Purchase #5	$180.87	12.110%	$202.7734	$202.77	$202.75	$202.80
Purchase #6	$182.88	8.423%	$198.284	$198.28	$198.30	$198.30
Purchase #7	$81.75	10.141%	$90.0403	$90.04	$90.05	$90.00
7 purchase totals =	$935.54		$1,040.5941	$1,040.59	$1,040.60	$1,040.60