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	$206.55	12.114%	$231.5715	$231.57	$231.55	$231.60
Purchase #2	$16.89	9.607%	$18.5126	$18.51	$18.50	$18.50
Purchase #3	$39.98	13.584%	$45.4109	$45.41	$45.40	$45.40
Purchase #4	$198.63	13.360%	$225.167	$225.17	$225.15	$225.20
Purchase #5	$221.85	9.472%	$242.8636	$242.86	$242.85	$242.90
Purchase #6	$111.84	12.557%	$125.8837	$125.88	$125.90	$125.90
Purchase #7	$213.36	4.481%	$222.9207	$222.92	$222.90	$222.90
7 purchase totals =	$1,009.10		$1,112.3300	$1,112.32	$1,112.25	$1,112.40