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	$50.73	9.364%	$55.4804	$55.48	$55.50	$55.50
Purchase #2	$146.59	3.570%	$151.8233	$151.82	$151.80	$151.80
Purchase #3	$82.86	13.445%	$94.0005	$94.00	$94.00	$94.00
Purchase #4	$182.33	11.349%	$203.0226	$203.02	$203.00	$203.00
Purchase #5	$160.32	11.281%	$178.4057	$178.41	$178.40	$178.40
Purchase #6	$67.90	7.466%	$72.9694	$72.97	$72.95	$73.00
Purchase #7	$125.96	4.751%	$131.9444	$131.94	$131.95	$131.90
7 purchase totals =	$816.69		$887.6463	$887.64	$887.60	$887.60