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	$212.39	4.467%	$221.8775	$221.88	$221.90	$221.90
Purchase #2	$150.78	12.387%	$169.4571	$169.46	$169.45	$169.50
Purchase #3	$67.32	11.751%	$75.2308	$75.23	$75.25	$75.20
Purchase #4	$58.31	4.817%	$61.1188	$61.12	$61.10	$61.10
Purchase #5	$86.32	9.340%	$94.3823	$94.38	$94.40	$94.40
Purchase #6	$38.56	10.234%	$42.5062	$42.51	$42.50	$42.50
Purchase #7	$169.36	13.206%	$191.7257	$191.73	$191.75	$191.70
7 purchase totals =	$783.04		$856.2984	$856.31	$856.35	$856.30