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	$150.69	9.665%	$165.2542	$165.25	$165.25	$165.30
Purchase #2	$53.88	5.430%	$56.8057	$56.81	$56.80	$56.80
Purchase #3	$170.65	11.488%	$190.2543	$190.25	$190.25	$190.30
Purchase #4	$37.34	9.860%	$41.0217	$41.02	$41.00	$41.00
Purchase #5	$198.31	11.791%	$221.6927	$221.69	$221.70	$221.70
Purchase #6	$110.33	5.798%	$116.7269	$116.73	$116.75	$116.70
Purchase #7	$197.57	9.794%	$216.92	$216.92	$216.90	$216.90
7 purchase totals =	$918.77		$1,008.6755	$1,008.67	$1,008.65	$1,008.70