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	$148.37	13.317%	$168.1284	$168.13	$168.15	$168.10
Purchase #2	$237.61	10.666%	$262.9535	$262.95	$262.95	$263.00
Purchase #3	$168.84	6.541%	$179.8838	$179.88	$179.90	$179.90
Purchase #4	$80.56	12.426%	$90.5704	$90.57	$90.55	$90.60
Purchase #5	$36.35	10.562%	$40.1893	$40.19	$40.20	$40.20
Purchase #6	$195.49	12.184%	$219.3085	$219.31	$219.30	$219.30
Purchase #7	$222.79	6.115%	$236.4136	$236.41	$236.40	$236.40
7 purchase totals =	$1,090.01		$1,197.4475	$1,197.44	$1,197.45	$1,197.50