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	$120.84	8.808%	$131.4836	$131.48	$131.50	$131.50
Purchase #2	$95.57	8.577%	$103.767	$103.77	$103.75	$103.80
Purchase #3	$246.82	8.664%	$268.2045	$268.20	$268.20	$268.20
Purchase #4	$250.89	9.577%	$274.9177	$274.92	$274.90	$274.90
Purchase #5	$203.89	8.807%	$221.8466	$221.85	$221.85	$221.80
Purchase #6	$90.46	10.492%	$99.9511	$99.95	$99.95	$100.00
Purchase #7	$247.85	12.471%	$278.7594	$278.76	$278.75	$278.80
7 purchase totals =	$1,256.32		$1,378.9299	$1,378.93	$1,378.90	$1,379.00