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	$23.93	13.250%	$27.1007	$27.10	$27.10	$27.10
Purchase #2	$145.95	13.288%	$165.3438	$165.34	$165.35	$165.30
Purchase #3	$212.71	9.217%	$232.3155	$232.32	$232.30	$232.30
Purchase #4	$145.71	6.179%	$154.7134	$154.71	$154.70	$154.70
Purchase #5	$189.92	3.221%	$196.0373	$196.04	$196.05	$196.00
Purchase #6	$36.98	3.548%	$38.2921	$38.29	$38.30	$38.30
Purchase #7	$174.31	4.702%	$182.5061	$182.51	$182.50	$182.50
7 purchase totals =	$929.51		$996.3089	$996.31	$996.30	$996.20