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	$41.59	10.399%	$45.9149	$45.91	$45.90	$45.90
Purchase #2	$55.77	5.833%	$59.0231	$59.02	$59.00	$59.00
Purchase #3	$210.68	9.626%	$230.9601	$230.96	$230.95	$231.00
Purchase #4	$214.92	13.287%	$243.4764	$243.48	$243.50	$243.50
Purchase #5	$38.87	3.831%	$40.3591	$40.36	$40.35	$40.40
Purchase #6	$249.59	10.141%	$274.9009	$274.90	$274.90	$274.90
Purchase #7	$91.66	11.119%	$101.8517	$101.85	$101.85	$101.90
7 purchase totals =	$903.08		$996.4862	$996.48	$996.45	$996.60