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	$36.63	3.429%	$37.886	$37.89	$37.90	$37.90
Purchase #2	$211.76	12.810%	$238.8865	$238.89	$238.90	$238.90
Purchase #3	$131.98	4.354%	$137.7264	$137.73	$137.75	$137.70
Purchase #4	$168.61	9.261%	$184.225	$184.23	$184.25	$184.20
Purchase #5	$246.72	9.666%	$270.568	$270.57	$270.55	$270.60
Purchase #6	$220.65	11.155%	$245.2635	$245.26	$245.25	$245.30
Purchase #7	$40.67	11.240%	$45.2413	$45.24	$45.25	$45.20
7 purchase totals =	$1,057.02		$1,159.7967	$1,159.81	$1,159.85	$1,159.80