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	$246.25	7.525%	$264.7803	$264.78	$264.80	$264.80
Purchase #2	$170.71	11.614%	$190.5363	$190.54	$190.55	$190.50
Purchase #3	$29.30	9.332%	$32.0343	$32.03	$32.05	$32.00
Purchase #4	$93.32	5.434%	$98.391	$98.39	$98.40	$98.40
Purchase #5	$78.98	12.700%	$89.0105	$89.01	$89.00	$89.00
Purchase #6	$8.40	10.179%	$9.255	$9.26	$9.25	$9.30
Purchase #7	$246.79	11.375%	$274.8624	$274.86	$274.85	$274.90
7 purchase totals =	$873.75		$958.8698	$958.87	$958.90	$958.90