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	$29.77	12.407%	$33.4636	$33.46	$33.45	$33.50
Purchase #2	$198.46	9.729%	$217.7682	$217.77	$217.75	$217.80
Purchase #3	$85.63	5.146%	$90.0365	$90.04	$90.05	$90.00
Purchase #4	$200.90	4.692%	$210.3262	$210.33	$210.35	$210.30
Purchase #5	$246.73	7.103%	$264.2552	$264.26	$264.25	$264.30
Purchase #6	$231.40	5.112%	$243.2292	$243.23	$243.25	$243.20
Purchase #7	$238.33	4.498%	$249.0501	$249.05	$249.05	$249.10
7 purchase totals =	$1,231.22		$1,308.1290	$1,308.14	$1,308.15	$1,308.20