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	$136.81	3.874%	$142.11	$142.11	$142.10	$142.10
Purchase #2	$130.91	5.495%	$138.1035	$138.10	$138.10	$138.10
Purchase #3	$128.75	6.812%	$137.5205	$137.52	$137.50	$137.50
Purchase #4	$140.99	4.814%	$147.7773	$147.78	$147.80	$147.80
Purchase #5	$77.27	5.469%	$81.4959	$81.50	$81.50	$81.50
Purchase #6	$135.63	4.310%	$141.4757	$141.48	$141.50	$141.50
Purchase #7	$60.33	12.532%	$67.8906	$67.89	$67.90	$67.90
7 purchase totals =	$810.69		$856.3735	$856.38	$856.40	$856.40