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	$51.46	6.676%	$54.8955	$54.90	$54.90	$54.90
Purchase #2	$82.82	5.808%	$87.6302	$87.63	$87.65	$87.60
Purchase #3	$53.82	13.694%	$61.1901	$61.19	$61.20	$61.20
Purchase #4	$191.78	9.169%	$209.3643	$209.36	$209.35	$209.40
Purchase #5	$38.57	4.437%	$40.2814	$40.28	$40.30	$40.30
Purchase #6	$80.70	5.623%	$85.2378	$85.24	$85.25	$85.20
Purchase #7	$249.36	4.695%	$261.0675	$261.07	$261.05	$261.10
7 purchase totals =	$748.51		$799.6668	$799.67	$799.70	$799.70