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	$115.76	13.353%	$131.2174	$131.22	$131.20	$131.20
Purchase #2	$169.98	12.597%	$191.3924	$191.39	$191.40	$191.40
Purchase #3	$158.96	7.811%	$171.3764	$171.38	$171.40	$171.40
Purchase #4	$80.63	11.635%	$90.0113	$90.01	$90.00	$90.00
Purchase #5	$195.79	3.448%	$202.5408	$202.54	$202.55	$202.50
Purchase #6	$232.53	5.196%	$244.6123	$244.61	$244.60	$244.60
Purchase #7	$169.45	7.769%	$182.6146	$182.61	$182.60	$182.60
7 purchase totals =	$1,123.10		$1,213.7652	$1,213.76	$1,213.75	$1,213.70