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	$96.26	3.611%	$99.7359	$99.74	$99.75	$99.70
Purchase #2	$74.66	10.460%	$82.4694	$82.47	$82.45	$82.50
Purchase #3	$84.76	12.129%	$95.0405	$95.04	$95.05	$95.00
Purchase #4	$143.85	13.192%	$162.8267	$162.83	$162.85	$162.80
Purchase #5	$245.89	5.641%	$259.7607	$259.76	$259.75	$259.80
Purchase #6	$141.33	8.787%	$153.7487	$153.75	$153.75	$153.70
Purchase #7	$225.69	5.294%	$237.638	$237.64	$237.65	$237.60
7 purchase totals =	$1,012.44		$1,091.2199	$1,091.23	$1,091.25	$1,091.10