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	$217.56	13.705%	$247.3766	$247.38	$247.40	$247.40
Purchase #2	$250.96	9.156%	$273.9379	$273.94	$273.95	$273.90
Purchase #3	$148.99	7.710%	$160.4771	$160.48	$160.50	$160.50
Purchase #4	$144.48	5.544%	$152.49	$152.49	$152.50	$152.50
Purchase #5	$110.86	6.268%	$117.8087	$117.81	$117.80	$117.80
Purchase #6	$152.31	12.614%	$171.5224	$171.52	$171.50	$171.50
Purchase #7	$131.33	10.498%	$145.117	$145.12	$145.10	$145.10
7 purchase totals =	$1,156.49		$1,268.7297	$1,268.74	$1,268.75	$1,268.70