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	$120.86	8.544%	$131.1863	$131.19	$131.20	$131.20
Purchase #2	$130.82	9.159%	$142.8018	$142.80	$142.80	$142.80
Purchase #3	$107.83	12.102%	$120.8796	$120.88	$120.90	$120.90
Purchase #4	$250.89	12.318%	$281.7946	$281.79	$281.80	$281.80
Purchase #5	$186.44	7.219%	$199.8991	$199.90	$199.90	$199.90
Purchase #6	$28.61	9.825%	$31.4209	$31.42	$31.40	$31.40
Purchase #7	$196.61	13.313%	$222.7847	$222.78	$222.80	$222.80
7 purchase totals =	$1,022.06		$1,130.7670	$1,130.76	$1,130.80	$1,130.80