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	$36.80	11.747%	$41.1229	$41.12	$41.10	$41.10
Purchase #2	$152.79	9.131%	$166.7413	$166.74	$166.75	$166.70
Purchase #3	$93.86	11.197%	$104.3695	$104.37	$104.35	$104.40
Purchase #4	$78.89	12.238%	$88.5446	$88.54	$88.55	$88.50
Purchase #5	$54.86	13.265%	$62.1372	$62.14	$62.15	$62.10
Purchase #6	$84.77	10.372%	$93.5623	$93.56	$93.55	$93.60
Purchase #7	$7.34	8.199%	$7.9418	$7.94	$7.95	$7.90
7 purchase totals =	$509.31		$564.4196	$564.41	$564.40	$564.30