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	$179.86	12.646%	$202.6051	$202.61	$202.60	$202.60
Purchase #2	$17.98	11.801%	$20.1018	$20.10	$20.10	$20.10
Purchase #3	$55.55	7.157%	$59.5257	$59.53	$59.55	$59.50
Purchase #4	$164.41	13.226%	$186.1549	$186.15	$186.15	$186.20
Purchase #5	$178.39	8.459%	$193.48	$193.48	$193.50	$193.50
Purchase #6	$131.94	7.215%	$141.4595	$141.46	$141.45	$141.50
Purchase #7	$120.91	12.740%	$136.3139	$136.31	$136.30	$136.30
7 purchase totals =	$849.04		$939.6409	$939.64	$939.65	$939.70