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	$29.74	13.808%	$33.8465	$33.85	$33.85	$33.80
Purchase #2	$229.96	9.138%	$250.9737	$250.97	$250.95	$251.00
Purchase #3	$123.90	13.711%	$140.8879	$140.89	$140.90	$140.90
Purchase #4	$229.84	3.869%	$238.7325	$238.73	$238.75	$238.70
Purchase #5	$189.63	5.437%	$199.9402	$199.94	$199.95	$199.90
Purchase #6	$221.40	9.219%	$241.8109	$241.81	$241.80	$241.80
Purchase #7	$56.38	6.127%	$59.8344	$59.83	$59.85	$59.80
7 purchase totals =	$1,080.85		$1,166.0261	$1,166.02	$1,166.05	$1,165.90