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	$58.44	12.595%	$65.8005	$65.80	$65.80	$65.80
Purchase #2	$63.44	13.148%	$71.7811	$71.78	$71.80	$71.80
Purchase #3	$208.27	4.807%	$218.2815	$218.28	$218.30	$218.30
Purchase #4	$203.72	8.531%	$221.0994	$221.10	$221.10	$221.10
Purchase #5	$116.28	6.741%	$124.1184	$124.12	$124.10	$124.10
Purchase #6	$96.98	9.185%	$105.8876	$105.89	$105.90	$105.90
Purchase #7	$245.51	7.666%	$264.3308	$264.33	$264.35	$264.30
7 purchase totals =	$992.64		$1,071.2993	$1,071.30	$1,071.35	$1,071.30