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	$215.48	3.199%	$222.3732	$222.37	$222.35	$222.40
Purchase #2	$177.88	12.280%	$199.7237	$199.72	$199.70	$199.70
Purchase #3	$78.73	3.309%	$81.3352	$81.34	$81.35	$81.30
Purchase #4	$27.28	7.764%	$29.398	$29.40	$29.40	$29.40
Purchase #5	$140.61	10.172%	$154.9128	$154.91	$154.90	$154.90
Purchase #6	$11.57	6.796%	$12.3563	$12.36	$12.35	$12.40
Purchase #7	$88.94	13.473%	$100.9229	$100.92	$100.90	$100.90
7 purchase totals =	$740.49		$801.0221	$801.02	$800.95	$801.00