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	$90.82	10.689%	$100.5277	$100.53	$100.55	$100.50
Purchase #2	$206.43	10.259%	$227.6077	$227.61	$227.60	$227.60
Purchase #3	$90.55	6.397%	$96.3425	$96.34	$96.35	$96.30
Purchase #4	$83.96	13.167%	$95.015	$95.02	$95.00	$95.00
Purchase #5	$84.48	3.801%	$87.6911	$87.69	$87.70	$87.70
Purchase #6	$240.57	10.236%	$265.1947	$265.19	$265.20	$265.20
Purchase #7	$175.98	5.244%	$185.2084	$185.21	$185.20	$185.20
7 purchase totals =	$972.79		$1,057.5871	$1,057.59	$1,057.60	$1,057.50