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	$67.88	13.763%	$77.2223	$77.22	$77.20	$77.20
Purchase #2	$115.66	13.678%	$131.48	$131.48	$131.50	$131.50
Purchase #3	$225.33	6.206%	$239.314	$239.31	$239.30	$239.30
Purchase #4	$185.84	6.676%	$198.2467	$198.25	$198.25	$198.20
Purchase #5	$24.85	12.234%	$27.8901	$27.89	$27.90	$27.90
Purchase #6	$116.52	3.789%	$120.9349	$120.93	$120.95	$120.90
Purchase #7	$98.74	6.157%	$104.8194	$104.82	$104.80	$104.80
7 purchase totals =	$834.82		$899.9074	$899.90	$899.90	$899.80