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	$91.67	7.800%	$98.8203	$98.82	$98.80	$98.80
Purchase #2	$37.26	9.559%	$40.8217	$40.82	$40.80	$40.80
Purchase #3	$98.58	11.458%	$109.8753	$109.88	$109.90	$109.90
Purchase #4	$249.34	7.612%	$268.3198	$268.32	$268.30	$268.30
Purchase #5	$127.39	9.207%	$139.1188	$139.12	$139.10	$139.10
Purchase #6	$120.96	3.262%	$124.9057	$124.91	$124.90	$124.90
Purchase #7	$231.59	11.735%	$258.7671	$258.77	$258.75	$258.80
7 purchase totals =	$956.79		$1,040.6287	$1,040.64	$1,040.55	$1,040.60