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	$37.27	5.536%	$39.3333	$39.33	$39.35	$39.30
Purchase #2	$43.40	9.501%	$47.5234	$47.52	$47.50	$47.50
Purchase #3	$201.50	7.220%	$216.0483	$216.05	$216.05	$216.00
Purchase #4	$185.73	13.150%	$210.1535	$210.15	$210.15	$210.20
Purchase #5	$171.50	5.226%	$180.4626	$180.46	$180.45	$180.50
Purchase #6	$91.34	13.761%	$103.9093	$103.91	$103.90	$103.90
Purchase #7	$250.37	5.114%	$263.1739	$263.17	$263.15	$263.20
7 purchase totals =	$981.11		$1,060.6043	$1,060.59	$1,060.55	$1,060.60