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	$45.84	7.529%	$49.2913	$49.29	$49.30	$49.30
Purchase #2	$129.47	9.224%	$141.4123	$141.41	$141.40	$141.40
Purchase #3	$175.98	13.664%	$200.0259	$200.03	$200.05	$200.00
Purchase #4	$234.43	4.276%	$244.4542	$244.45	$244.45	$244.50
Purchase #5	$127.71	7.186%	$136.8872	$136.89	$136.90	$136.90
Purchase #6	$156.72	11.322%	$174.4638	$174.46	$174.45	$174.50
Purchase #7	$54.59	8.544%	$59.2542	$59.25	$59.25	$59.30
7 purchase totals =	$924.74		$1,005.7889	$1,005.78	$1,005.80	$1,005.90