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	$73.55	6.307%	$78.1888	$78.19	$78.20	$78.20
Purchase #2	$131.38	6.169%	$139.4848	$139.48	$139.50	$139.50
Purchase #3	$203.34	7.315%	$218.2143	$218.21	$218.20	$218.20
Purchase #4	$212.94	13.326%	$241.3164	$241.32	$241.30	$241.30
Purchase #5	$196.61	11.774%	$219.7589	$219.76	$219.75	$219.80
Purchase #6	$162.68	7.252%	$174.4776	$174.48	$174.50	$174.50
Purchase #7	$133.29	6.133%	$141.4647	$141.46	$141.45	$141.50
7 purchase totals =	$1,113.79		$1,212.9055	$1,212.90	$1,212.90	$1,213.00