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	$123.36	5.299%	$129.8968	$129.90	$129.90	$129.90
Purchase #2	$85.74	5.586%	$90.5294	$90.53	$90.55	$90.50
Purchase #3	$35.55	10.806%	$39.3915	$39.39	$39.40	$39.40
Purchase #4	$218.95	11.348%	$243.7964	$243.80	$243.80	$243.80
Purchase #5	$208.89	7.434%	$224.4189	$224.42	$224.40	$224.40
Purchase #6	$69.95	12.589%	$78.756	$78.76	$78.75	$78.80
Purchase #7	$119.46	9.680%	$131.0237	$131.02	$131.00	$131.00
7 purchase totals =	$861.90		$937.8127	$937.82	$937.80	$937.80