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	$65.36	10.597%	$72.2862	$72.29	$72.30	$72.30
Purchase #2	$135.71	5.287%	$142.885	$142.89	$142.90	$142.90
Purchase #3	$75.72	5.790%	$80.1042	$80.10	$80.10	$80.10
Purchase #4	$248.37	8.167%	$268.6544	$268.65	$268.65	$268.70
Purchase #5	$172.57	5.779%	$182.5428	$182.54	$182.55	$182.50
Purchase #6	$187.42	11.643%	$209.2413	$209.24	$209.25	$209.20
Purchase #7	$47.64	12.216%	$53.4597	$53.46	$53.45	$53.50
7 purchase totals =	$932.79		$1,009.1736	$1,009.17	$1,009.20	$1,009.20