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	$184.76	3.839%	$191.8529	$191.85	$191.85	$191.90
Purchase #2	$137.94	12.272%	$154.868	$154.87	$154.85	$154.90
Purchase #3	$35.34	3.365%	$36.5292	$36.53	$36.55	$36.50
Purchase #4	$141.88	7.788%	$152.9296	$152.93	$152.95	$152.90
Purchase #5	$188.35	6.227%	$200.0786	$200.08	$200.10	$200.10
Purchase #6	$224.92	12.627%	$253.3206	$253.32	$253.30	$253.30
Purchase #7	$21.92	3.151%	$22.6107	$22.61	$22.60	$22.60
7 purchase totals =	$935.11		$1,012.1896	$1,012.19	$1,012.20	$1,012.20