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	$224.90	11.241%	$250.181	$250.18	$250.20	$250.20
Purchase #2	$99.33	11.330%	$110.5841	$110.58	$110.60	$110.60
Purchase #3	$48.68	13.654%	$55.3268	$55.33	$55.35	$55.30
Purchase #4	$25.39	10.151%	$27.9673	$27.97	$27.95	$28.00
Purchase #5	$161.60	4.295%	$168.5407	$168.54	$168.55	$168.50
Purchase #6	$169.85	12.695%	$191.4125	$191.41	$191.40	$191.40
Purchase #7	$109.89	7.322%	$117.9361	$117.94	$117.95	$117.90
7 purchase totals =	$839.64		$921.9485	$921.95	$922.00	$921.90