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	$131.38	3.874%	$136.4697	$136.47	$136.45	$136.50
Purchase #2	$117.42	6.330%	$124.8527	$124.85	$124.85	$124.90
Purchase #3	$86.38	6.294%	$91.8168	$91.82	$91.80	$91.80
Purchase #4	$141.82	10.222%	$156.3168	$156.32	$156.30	$156.30
Purchase #5	$229.33	5.430%	$241.7826	$241.78	$241.80	$241.80
Purchase #6	$28.43	12.171%	$31.8902	$31.89	$31.90	$31.90
Purchase #7	$168.59	13.358%	$191.1103	$191.11	$191.10	$191.10
7 purchase totals =	$903.35		$974.2391	$974.24	$974.20	$974.30