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	$114.45	8.237%	$123.8772	$123.88	$123.90	$123.90
Purchase #2	$160.50	11.601%	$179.1196	$179.12	$179.10	$179.10
Purchase #3	$140.48	3.604%	$145.5429	$145.54	$145.55	$145.50
Purchase #4	$246.39	12.123%	$276.2599	$276.26	$276.25	$276.30
Purchase #5	$183.63	3.320%	$189.7265	$189.73	$189.75	$189.70
Purchase #6	$91.98	12.312%	$103.3046	$103.30	$103.30	$103.30
Purchase #7	$238.46	12.528%	$268.3343	$268.33	$268.35	$268.30
7 purchase totals =	$1,175.89		$1,286.1650	$1,286.16	$1,286.20	$1,286.10