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	$248.47	6.790%	$265.3411	$265.34	$265.35	$265.30
Purchase #2	$112.41	6.652%	$119.8875	$119.89	$119.90	$119.90
Purchase #3	$20.34	9.307%	$22.233	$22.23	$22.25	$22.20
Purchase #4	$89.35	11.154%	$99.3161	$99.32	$99.30	$99.30
Purchase #5	$68.61	5.299%	$72.2456	$72.25	$72.25	$72.20
Purchase #6	$5.51	6.659%	$5.8769	$5.88	$5.90	$5.90
Purchase #7	$225.73	10.468%	$249.3594	$249.36	$249.35	$249.40
7 purchase totals =	$770.42		$834.2596	$834.27	$834.30	$834.20