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	$165.86	11.780%	$185.3983	$185.40	$185.40	$185.40
Purchase #2	$103.38	6.309%	$109.9022	$109.90	$109.90	$109.90
Purchase #3	$225.38	3.108%	$232.3848	$232.38	$232.40	$232.40
Purchase #4	$76.41	6.541%	$81.408	$81.41	$81.40	$81.40
Purchase #5	$141.68	8.826%	$154.1847	$154.18	$154.20	$154.20
Purchase #6	$240.98	12.322%	$270.6736	$270.67	$270.65	$270.70
Purchase #7	$42.68	11.534%	$47.6027	$47.60	$47.60	$47.60
7 purchase totals =	$996.37		$1,081.5543	$1,081.54	$1,081.55	$1,081.60