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	$212.78	12.705%	$239.8137	$239.81	$239.80	$239.80
Purchase #2	$152.33	12.760%	$171.7673	$171.77	$171.75	$171.80
Purchase #3	$69.70	12.161%	$78.1762	$78.18	$78.20	$78.20
Purchase #4	$160.69	13.270%	$182.0136	$182.01	$182.00	$182.00
Purchase #5	$63.75	11.807%	$71.277	$71.28	$71.30	$71.30
Purchase #6	$218.64	6.655%	$233.1905	$233.19	$233.20	$233.20
Purchase #7	$52.76	4.378%	$55.0698	$55.07	$55.05	$55.10
7 purchase totals =	$930.65		$1,031.3081	$1,031.31	$1,031.30	$1,031.40