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	$72.84	10.152%	$80.2347	$80.23	$80.25	$80.20
Purchase #2	$38.92	9.871%	$42.7618	$42.76	$42.75	$42.80
Purchase #3	$123.61	6.503%	$131.6484	$131.65	$131.65	$131.60
Purchase #4	$218.80	11.118%	$243.1262	$243.13	$243.15	$243.10
Purchase #5	$189.80	13.676%	$215.757	$215.76	$215.75	$215.80
Purchase #6	$135.32	11.262%	$150.5597	$150.56	$150.55	$150.60
Purchase #7	$16.58	9.240%	$18.112	$18.11	$18.10	$18.10
7 purchase totals =	$795.87		$882.1998	$882.20	$882.20	$882.20