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	$57.48	6.423%	$61.1719	$61.17	$61.15	$61.20
Purchase #2	$182.43	11.666%	$203.7123	$203.71	$203.70	$203.70
Purchase #3	$155.64	5.674%	$164.471	$164.47	$164.45	$164.50
Purchase #4	$35.45	5.409%	$37.3675	$37.37	$37.35	$37.40
Purchase #5	$161.40	3.365%	$166.8311	$166.83	$166.85	$166.80
Purchase #6	$81.45	12.298%	$91.4667	$91.47	$91.45	$91.50
Purchase #7	$242.83	3.296%	$250.8337	$250.83	$250.85	$250.80
7 purchase totals =	$916.68		$975.8542	$975.85	$975.80	$975.90