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	$36.27	4.115%	$37.7625	$37.76	$37.75	$37.80
Purchase #2	$63.61	10.634%	$70.3743	$70.37	$70.35	$70.40
Purchase #3	$229.53	7.790%	$247.4104	$247.41	$247.40	$247.40
Purchase #4	$142.54	4.182%	$148.501	$148.50	$148.50	$148.50
Purchase #5	$219.78	9.535%	$240.736	$240.74	$240.75	$240.70
Purchase #6	$243.27	12.332%	$273.2701	$273.27	$273.25	$273.30
Purchase #7	$66.64	8.184%	$72.0938	$72.09	$72.10	$72.10
7 purchase totals =	$1,001.64		$1,090.1481	$1,090.14	$1,090.10	$1,090.20