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	$30.58	3.362%	$31.6081	$31.61	$31.60	$31.60
Purchase #2	$234.34	3.812%	$243.273	$243.27	$243.25	$243.30
Purchase #3	$165.97	4.560%	$173.5382	$173.54	$173.55	$173.50
Purchase #4	$139.47	12.801%	$157.3236	$157.32	$157.30	$157.30
Purchase #5	$141.90	11.443%	$158.1376	$158.14	$158.15	$158.10
Purchase #6	$91.27	11.372%	$101.6492	$101.65	$101.65	$101.60
Purchase #7	$128.55	12.185%	$144.2138	$144.21	$144.20	$144.20
7 purchase totals =	$932.08		$1,009.7435	$1,009.74	$1,009.70	$1,009.60