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	$50.75	13.136%	$57.4165	$57.42	$57.40	$57.40
Purchase #2	$135.61	12.623%	$152.7281	$152.73	$152.75	$152.70
Purchase #3	$158.54	3.510%	$164.1048	$164.10	$164.10	$164.10
Purchase #4	$67.45	7.799%	$72.7104	$72.71	$72.70	$72.70
Purchase #5	$125.29	13.223%	$141.8571	$141.86	$141.85	$141.90
Purchase #6	$183.33	3.146%	$189.0976	$189.10	$189.10	$189.10
Purchase #7	$240.80	13.504%	$273.3176	$273.32	$273.30	$273.30
7 purchase totals =	$961.77		$1,051.2321	$1,051.24	$1,051.20	$1,051.20